Gadget Freak

Circuit Design Idea - Low-cost circuit incorporates mixing and amplifying functions

2008-07-23T10:18:17Z

Check out another newly-uploaded Design Idea designed to give circuit building inspiration.

It covers frequency-conversion, and optimising the mixer function with the amplifier, with two resistors in the feedback loop setting the voltage-conversion gain.

The Design Idea begins:

In many applications, the frequency-conversion steps comprise a buffer, preferably with some extra voltage gain; a mixer; and some filtering. Instead of including an amplifier in front of the mixer, you can easily integrate the mixer function with the amplifier.

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In many applications, the frequency-conversion steps comprise a buffer, preferably with some extra voltage gain; a mixer; and some filtering. Instead of including an amplifier in front of the mixer, you can easily integrate the mixer function with the amplifier.

A low-cost implementation uses an amplifier with a power-down-disable feature. When a square-wave local oscillator drives the disable pin, a square wave at the oscillator's frequency multiplies the input signal, and frequency conversion takes place.

Read the full Circuit Design Idea

It is courtesy of Guus Colman, Guy Torfs, Johan Bauwelinck, and Jan Vandewege of INTEC/IMEC, Ghent University (Edited by Martin Rowe and Fran Granville of EDN).

View all the Design Ideas on Electronics Weekly

Hans' Nixie clock takes a step back in time

2008-07-21T08:37:29Z

Back in the days of the Berlin Wall, these Nixie tubes were manufactured by a now long-forgotten company. Fast forward to the twenty-first century, and Hans Summers found them stocked by an antique electronics part company.

Originally painted red, the coating from the 4-inch high tubes were painstakingly removed using a craft knife. Using a plain matrix board and wire connections, Hans built the circuit on three boards.

The first holds the rectifier, divide by 50 circuit, seconds counters and seconds driver transistors. The second and third boards hold the counters and drivers for the minutes and hours digit pairs. Now your tribute to East Germany is sure to get past Checkpoint Charlie.

You can read the full details of the project, including a data sheet for the Z568M and details of the construction, on Hans' website.

The Nixie tube

Hans used the Z568M, which is 4-inches high (100mm) and has a digit height of 2 inches (50mm). It is therefore truly a giant amongst nixie tubes, he says, presumably intended for railway clock applications and so on.

]]> Back in the days of the Berlin Wall, these Nixie tubes were manufactured by a now long-forgotten company. Fast forward to the twenty-first century, and Hans Summers found them stocked by an antique electronics part company.

Originally painted red, the coating from the 4-inch high tubes were painstakingly removed using a craft knife. Using a plain matrix board and wire connections, Hans built the circuit on three boards.

The first holds the rectifier, divide by 50 circuit, seconds counters and seconds driver transistors. The second and third boards hold the counters and drivers for the minutes and hours digit pairs. Now your tribute to East Germany is sure to get past Checkpoint Charlie.

You can read the full details of the project, including a data sheet for the Z568M and details of the construction, on Hans' website.

The Nixie tube

Hans used the Z568M, which is 4-inches high (100mm) and has a digit height of 2 inches (50mm). It is therefore truly a giant amongst nixie tubes, he says, presumably intended for railway clock applications and so on.

It is painted red to improve the contrast. There is also a non-coated version available, the Z5680M, but he could not obtain any at that time. Hans writes that because he finds the internal construction of nixies very beautiful, he removed the paint using a craft knife. It was a long and tedious process during which I was constantly afraid of breaking the tubes, particularly when excavating the seal at the top of the tube.

Construction

Hans writes: I did not use a printed circuit board (PCB), instead I used my favourite method of construction, which is plain matrix board and wire connections. The circuit is built on three circuit boards. The first holds the rectifier, divide by 50 circuit, seconds counters and seconds driver transistors. The second and third boards hold the counters and drivers for the minutes and hours digit pairs.

The nixies are mounted in pairs on single-sided PCB material. I placed the copper side upwards, and drilled holes to match the nixie base. The nixie pins are pushed through the holes and soldered to wires on the underside. It is probably better to use sockets for the nixies but the Z568M is a very large nixie for which I doubt ordinary sockets are available. It is possible to build your own sockets but I opted for direct soldering, though this must be done with extreme care not to crack the glass. The central nixie pair (minutes) has two PCB-material pillars which the colon neons are attached to, with their 100K series resistors. The circuit board for each pair is attached behind the nixie tubes at right angles to the nixie boards, using triangular cuts of PCB material.

Circuit

"I used a very similar circuit to Mike's nixie clock (http://www.electricstuff.co.uk/), writes Hans. "Mine is a 6-digit clock, i.e. has an extra pair of nixies for the seconds. I made a few very minor modifications to the circuit.

"I moved the seconds hold switch to earlier in the counter chain, because I found that otherwise a full second did not elapse between letting go of the switch and the seconds being incremented. Since my clock display seconds, I also connected the colon nixies to be on continuously.

"I omitted any form of mains isolation, in the interests of living dangerously (do this at your own risk!). I found a series resistance of 22K to be about right for the Z568M, but they overheated so I replaced them with two 47K resistors in parallel (23.5K).

"The total cost of the electronic parts for this circuit (excluding the nixies) was under UK £10. Of course, the nixies are very expensive, and the materials for the cabinet."

View a full size circuit diagram (1188 x 873, 95K)

Parts List

6x NIXIE tubes from eBay or similar
4x Neon bulb
8x 4017 integrated circuit
1x 4013 integrated circuit
44x MPSA42
1x 5.1V zener diode
5x 1N4004 diode
44x 33K resistor
12x 47K resistor
7x 100K resistor
1x 2.2M resistor
2x 10K resistor
1x 68K resistor
1x 470uF capacitor
1x 100nF capacitor
3x 1nF capacitor
1x 100pF capacitor
3x reed switch
1x bar magnet
1x isolating transformer

Hans notes: Of course, the nixies are obsolete. The giant E.German Z568's I used are very hard to find but substitutes and smaller nixies are readily available. The 12 resistors which I have marked as 47K would need to be increased for smaller nixies, but I will refer to this in the text.

Nixie history

For more background on Nixie clocks, including the history of Nixie tubes, see NixieClock.net

"Nixie tubes were originally developed in 1952 by the Haydu brothers for the Burroughs Corporation..."

Getting a charge from broken solar panels

2008-07-17T15:14:14Z

Charging any device under the sun, when out in the wilds... with credit to GreenerBusinessShow.org
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Charging any device under the sun, when out in the wilds...

Credit to GreenerBusinessShow.org for this excellently producted video, showing how they soldered together pieces of broken solar panels, enabling them to function as an AA battery charger, producing "about 6 volts in direct sunlight and about 3 volts indoors".

Parts list:

broken solar panels
1.5 ounce silver-bearing solder
rectifier diode
thin stranded copperwire

According to the site, GreenerBusinessShow is "a podcast about making business of all kind environmentally friendly, with simple tips guides, and how-tos". It is part of the non-profit R.C Cosmos.

LED Jellyfish Mood Lamp

2008-07-16T15:45:50Z

Welcome to the "hypnotic, other-worldly appeal of the LED Jellyfish Mood Lamp".

This press release has just caught my attention - a light-hearted one for Gadget Freak, I thought.

How much of a challenge would it be to recreate such a device?... (The real challenge would be in circulating the jellyfish in an interesting manner, I think, rather than the lighting effect)

The ambient lighting device is described as having a "whisper-quiet" operation and features an auto-off safety function that kicks in after four hours of use.

]]> Welcome to the "hypnotic, other-worldly appeal of the LED Jellyfish Mood Lamp".

This press release has just caught my attention - a light-hearted one for Gadget Freak, I thought.

How much of a challenge would it be to recreate such a device, I wonder... (the real challenge would be in circulating the jellyfish in an interesting manner, rather than the lighting effect, IMHO)

The ambient lighting device is described as having a "whisper-quiet" operation and features an auto-off safety function that kicks in after four hours of use.

You simply fill the moulded black tank with water, chuck in the jellyfish, fit the top and plug in. If you want single-colour jelly fish, rather than a changing sequence of colour, you flick a switch...

The device, with a RRP of £29.99, is from BB Trade Sales (the self-styled "place to shop for electronic gadgets, boys toys and gadgets").

See the full Gadget Freak LED Archives

Sign up for the newsletter

2008-07-16T12:10:29Z

Having one of those days? Work driving you mad? Just can't seem to find the time to visit Gadget Freak as much as you would like to?

Well, don't stress, help is at hand. If you can't come to us, we'll come to you!

You can now sign up for the Circuits newsletter to ensure you receive the latest and greatest Gadget Freak news, hot and fresh, straight into your inbox!

Signing up only takes a second and then you can sit back and relax as we do the rest.

]]>

Having one of those days? Work driving you mad? Just can't seem to find the time to visit Gadget Freak as much as you would like to?

Well, don't stress, help is at hand. If you can't come to us, we'll come to you!

You can now sign up for the Circuits newsletter to ensure you receive the latest and greatest Gadget Freak news, hot and fresh, straight into your inbox!

Signing up only takes a second and then you can sit back and relax as we do the rest.

Go on, sign up - it will be the best decision you've ever made!

Circuit Design Idea - Simple blown-fuse indicator sounds an alarm

2008-07-15T14:56:28Z

Here's a newly-uploaded Design Idea to help give circuit building inspiration.

It relates to blown-fuses, and creating an indicating circuit that will warn you of failure, important when the fuse body is ceramic or sand-filled for improved protection against arcing.

The Design Idea begins:

Safety fuses or fusible links see wide use in modern electronic equipment to protect the load and the power supply - especially batteries - against short circuits and excessive load current. Fuses are inexpensive and simple, and a wide range of parts is available.

]]> Here's a newly-uploaded Design Idea to help give circuit building inspiration.

It relates to blown-fuses, and creating an indicating circuit that will warn you of failure, important when the fuse body is ceramic or sand-filled for improved protection against arcing.

The Design Idea begins:

Safety fuses or fusible links see wide use in modern electronic equipment to protect the load and the power supply - especially batteries - against short circuits and excessive load current. Fuses are inexpensive and simple, and a wide range of parts is available.

However, you must replace them when they blow, and, when they do, you need an indicating circuit that warns you about its failure, especially when the fuse body is ceramic or sand-filled for improved protection against arcing. The circuit in Figure 1 (PDF) signals that a fuse has blown. Input voltage ranges from 4 to 30V dc. The input range of the 78L05 voltage regulator determines the high limit; the lower one is less than the input range of the voltage regulator, but 4V dc is sufficient for the indicator to operate.

Read the full Circuit Design Idea

It is courtesy of Vladimir Oleynik (edited by Martin Rowe and Fran Granville - EDN).

View all the Design Ideas on Electronics Weekly

Project Dragon Fish - Underwater Rocket Science

2008-07-11T13:22:08Z

Thanks to Design News for this Gadget Freak, in which one Joe Peck takes (model) rocket science down to watery depths.

Editor's Note: Please read the safety instructions in the build instructions document carefully!

We quote:

"Joe Peck has extended the pursuit of realism in model rocketry to the launch environment. Think Poseidon here - this rocket launches from underwater. Initially, it's sealed watertight from nose to nozzle.

Ignition is triggered by bringing a magnet close to a sensor contained in the upper section. The motor ignites, blowing off the bottom end cap and we have liftoff! If you're into model rocketry, here's your next challenge."

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"Joe Peck has extended the pursuit of realism in model rocketry to the launch environment. Think Poseidon here - this rocket launches from underwater. Initially, it's sealed watertight from nose to nozzle.

Ignition is triggered by bringing a magnet close to a sensor contained in the upper section. The motor ignites, blowing off the bottom end cap and we have liftoff! If you're into model rocketry, here's your next challenge."

Parts List

Amt	Part Description
1	9V battery connector
1	Magnetic Switch (normally open)
1	MOSFET, IRFU3704Z
1	1 k ohm, 1/4W resistor

Additional parts required
Receptade (2 position)
Magnet
9V NiCad battery

Download the build instructions for Joe's model rocketry (Word file)

You can also watch a video of Joe's work

Charlieplexing - Cylon-eyes and Holoclocks

2008-07-07T07:10:25Z

Charlieplexing. The verb is an electronics technique apparently named after one Charlie Allen, an engineer at Maxim.

It involves minimising the use of I/O pins on a microcontroller to drive a maximum number of LEDs, for example using the same pin to alternate between driving digits (cathodes) and segments (anodes).

You can read an entry on Charlieplexing in Wikipedia. I quote:

"Much like standard multiplexed displays, all the cathodes of any particular digit are connected together to a single I/O pin which remains low. Much like standard multiplexed displays, each anode of each LED of a particular digit is tied to the current-limiting resistor of a different I/O pin.

]]>

Charlieplexing. The verb is an electronics technique apparently named after one Charlie Allen, an engineer at Maxim.

It involves minimising the use of I/O pins on a microcontroller to drive a maximum number of LEDs, for example using the smae pin to alternate between driving digits (cathodes) and segments (anodes).

You can read an entry on Charlieplexing in Wikipedia. I quote:

"Much like standard multiplexed displays, all the cathodes of any particular digit are connected together to a single I/O pin which remains low. Much like standard multiplexed displays, each anode of each LED of a particular digit is tied to the current-limiting resistor of a different I/O pin.

During operation, only one of the I/O pins is pulled low at any one time, pulling the cathodes of one particular digit low, acting like the digit-select line of standard multiplexed displays. All the other I/O pins connected to the display act as the "segment select" "anode pins" of a standard multiplexed display. All those pins are either "enabled" (pulled high through the current-limiting resistor) or "disabled" (aka "left disconnected" or "high Z" or "direction=input")."

Maxim themselves simply define Charlieplexing as "a display driver circuit to reduce pin-count". Its a multiplexing technique used in their own LED display drivers, and you can read an Application Note from the company on this particular topic.

Do a search on YouTube and you will find plenty of examples.

Here is one - "Cylon-eye" (based on the Galactica Android characters) - using an ATtiny15L AVR microcontroller (a circuit diagram and more info is on the site),

Here is another impressive one, involving what its inventor dubbs a 'Holoclock', where randomly changing LED patterns are used to indicate the time. Very cool, even if hard to see the time at a glance. (Again, circuit info and description available via the link)

(Different colours are assigned to different digits, red = 10 hours, amber = hour, green = 10 minutes, blue = minute, so 12:07 would be one red, two amber, no green and seven blue....). Very clever, but definitely not a quick and easy way to glance the time...

The inventor, (rgbphil), writes:

"A 20Mhz crystal has been added to the Microdot circuit to clock the PIC much faster, this allows the array to be scanned faster and enables the implementation of a dimming algorithm. The dimming algorithm was very important to getting a cross pattern fade and ambient light function to work. This would have been impossible with the Microdot, because of the slower clock speed as some scan cycles needed to be spent on dimming. See next section for a description of the Dimming functionality.

"The other things to note are the use of a MCP1252 charge pump regulator to supply 5V, my favourite chip at the moment. If you modified the circuit you could use a plain old 7805......I just have a number of these handy chips hanging around."

Fascinating stuff!

When robots swarm

2008-07-02T13:42:09Z

Run for the hills, the robots are coming!

Found this one on YouTube after looking into the work done at the Laboratory of Intelligent Systems at EPFL (École Polytechnique Fédérale de Lausanne).

They came to my attention via an eye-snagging story on EDN, our American sister site - Robotic grasshopper leaps as high as 27 times its height. The researchers in Switzerland have apparently built a 5cm-tall robot, based on grasshoppers and locusts, that can jump as high as 1.4m.

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Run for the hills, the robots are coming!

Found this one on YouTube after looking into the work done at the Laboratory of Intelligent Systems at EPFL (École Polytechnique Fédérale de Lausanne).

They came to my attention via an eye-snagging story on EDN, our American sister site - Robotic grasshopper leaps as high as 27 times its height. The researchers in Switzerland have apparently built a 5cm-tall robot, based on grasshoppers and locusts, that can jump as high as 1.4m.

The non-sentient being uses a 0.6g pager motor to slowly charge two torsion springs and then explosively release that energy.

The device's battery, it says, can power 320 jumps at 3-sec intervals).

You can see a video related to their work below. Interesting stuff, but with a slightly sinister undertow!

Circuit Design Ideas - CMOS DACs act as digitally controlled voltage divider

2008-07-01T09:31:35Z

Another Design idea to get your circuit synapses firing.

While digital potentiometers can make excellent digitally controlled voltage dividers in applications in which 8-bit resolution is acceptable, this circuit shows how to use a CMOS DAC as a voltage divider in applications requiring higher resolution.

The Design Idea begins:

"Millions of CMOS R2R (resistor/two-resistor)-ladder DACs have found use in attenuator applications in which an external op amp acting as a current-to-voltage converter forces one current-output terminal to a virtual ground. The reference input to the DAC can be ac or dc as long as the op amp can produce the desired output voltage. A phase inversion is normal between input and output, so the circuit requires dual power supplies."

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"Millions of CMOS R2R (resistor/two-resistor)-ladder DACs have found use in attenuator applications in which an external op amp acting as a current-to-voltage converter forces one current-output terminal to a virtual ground. The reference input to the DAC can be ac or dc as long as the op amp can produce the desired output voltage. A phase inversion is normal between input and output, so the circuit requires dual power supplies."

"Figure 1 shows a way to rewire this simple circuit to avoid the phase inversion and to operate with a single supply. In this configuration, the DAC acts as a digitally programmable resistor, and the DAC's code changes the effective resistance between the input voltage and the IOUT1 output-current terminal of the DAC."

Read the full Circuit Design Idea

It is courtesy of John Wynne and Liam Riordan, of Analog Devices in Limerick, Ireland (edited by Martin Rowe and Fran Granville of EDN).

View all the Design Ideas on Electronics Weekly

Vote for Best Gadget Freak of the Year

2008-06-26T13:07:09Z

During the past year, Gadget Freak has highlighted each month 12 unique and wonderful inventions, ranging from an alarm to remind you to close the fridge door through to a device that's specially designed to produce theatrical special effects, like a confetti rainstorm.

Now we put the fate of these gadgets in your hands. Have your say, and vote for your 'Best of the Year' Gadget Freak!

Best of luck to all the 12 entrants and be ready to witness the crowning of the first Gadget Freak of the Year!

Simply email webmaster@electronicsweekly.com and state the month of your choice.

]]>

Now we put the fate of these gadgets in your hands. Have your say, and vote for your 'Best of the Year' Gadget Freak!

Best of luck to all the 12 entrants and be ready to witness the crowning of the first Gadget Freak of the Year!

Simply email webmaster@electronicsweekly.com and state the month of your choice.

Gadget Freak of the Year
Jun 07 - Clive had an engagingly surreal stage presence	Jul 07 - Hans knows the truth is out there
Aug 07 - Some fridges are always alarmed	Sep 07 - Guido knew the secret to a perfect cuppa
Oct 07 - Meet Andrew's blast from the past	Nov 07 - Keep your PC cool this winter
Dec 07 - Jon knows how to spread Christmas cheer	Jan 08 - Richard had a flash of inspiration
Feb 08 - Pete decided to give his lamp a facelift	Mar 08 - Andrew liked the sound of nostalgia
Apr 08 - CMOS quad Schmitt makes gardening easy	May 08 - Keep your property where you can see it

Remember, simply email webmaster@electronicsweekly.com and state the month of your choice. Voting will close after Friday 25 July.

Circuit Design Ideas - Programmable current source, Composite instrumentation amplifier

2008-06-26T09:39:19Z

Possible sparks for your inspiration, when it comes to designing your own circuits. Two more Circuit Design Ideas that have been added to the site.

They involve an easy-to-build, easy-to-use, low-cost current source, and a composite instrumentation amplifier.

Programmable current source requires no power supply, courtesy of John Guy, National Semiconductor; Edited by Charles H Small and Fran Granville

Composite instrumentation amplifier challenges single-chip device for bandwidth, offset, and noise, courtesy of Marián Štofka, Slovak University of Technology, Bratislava, Slovakia; Edited by Charles H Small and Fran Granville

]]> Possible sparks for your inspiration, when it comes to designing your own circuits. Two more Circuit Design Ideas that have been added to the site.

They involve an easy-to-build, easy-to-use, low-cost current source, and a composite instrumentation amplifier.

Programmable current source requires no power supply, courtesy of John Guy, National Semiconductor; Edited by Charles H Small and Fran Granville

Composite instrumentation amplifier challenges single-chip device for bandwidth, offset, and noise, courtesy of Marián Štofka, Slovak University of Technology, Bratislava, Slovakia; Edited by Charles H Small and Fran Granville

Programmable current source requires no power supply
Engineering labs are usually equipped with various power supplies, voltmeters, function generators, and oscilloscopes. One piece of equipment missing from many such labs, however, is a current source. This omission is unfortunate, because a current source is useful for creating I-V (current-versus-voltage) curves, charging and discharging batteries, preloading power supplies, and many other applications.

The circuit in Figure 1 is an easy-to-build, easy-to-use, low-cost current source. It comprises three sections of BCD (binary-coded-decimal) switches, a three-terminal adjustable regulator, a handful of 1%-tolerant resistors, and a National Semiconductor LM317 three-terminal adjustable regulator.
Read the full Circuit Design Idea

Composite instrumentation amplifier challenges single-chip device for bandwidth, offset, and noise
Although the prevailing number set in electronics is binary, human-machine interaction uses a decimal-number set. For this reason, designs often require the use of amplifiers with gain programmable in steps in the power of 10. Currently, Analog Devices' AD8253 monolithic instrumentation amplifier is digitally programmable with voltage gains of one, 10, 100, and 1000 (Reference 1).

This IC has high bandwidth at lower gains, but you inevitably sacrifice this bandwidth when the amplifier has a gain of 1000. If your application's demands for bandwidth reach the megahertz range at a gain of 1000 and if offset and noise performance prevail over circuit complexity, then a composite amplifier may fill the bill (Figure 1).
Read the full Circuit Design Idea

Manly speakers

2008-06-23T07:19:47Z

Exploring around the Instructables site, this self-amended gadget caught my eye - Munny Speakers.

The phenomenon of modifiable Munnys ("The Greatest Do It Yourself Toy") has escaped my attention - perhaps the parents among you are already too familiar with these - but the application here is quite obvious.

"Give your speakers some extra personality by making them out of a vinyl doll. Kid Robot makes the easily hackable Munny doll and I've been meaning to cut one up. The combined need for some new speakers created a happy union of doll and speaker," writes fungus amungus.

]]> Exploring around the Instructables site, this self-amended gadget caught my eye - Munny Speakers.

The phenomenon of modifiable Munnys ("The Greatest Do It Yourself Toy") has escaped my attention - perhaps the parents among you are already too familiar with these - but the application here is quite obvious.

"Give your speakers some extra personality by making them out of a vinyl doll. Kid Robot makes the easily hackable Munny doll and I've been meaning to cut one up. The combined need for some new speakers created a happy union of doll and speaker," writes fungus amungus.

"The vinyl that the Munny is made of is pretty firm when it's at room temperature, but heat it up with a hair dryer or a heat gun and it softens up oh so nicely. After that the Xacto cuts through it like butter."

BTW - sorry I can't resist the plug - check out our recent guide to Digital technology and loudspeaker design. Featuring Bowers and Wilkins, and their £40,000 top-of-the-range Nautilus speakers, this covers slightly different territory to our Munnys.

We wrote: "These are huge speakers, 1.2m tall, so there is no need for reflex ports to boost bass response. Instead there is a tube attached to the rear of each driver to remove rearward energy. The tube is filled with absorbent material and shaped to taper the sound to zero at the far end. "It is like a horn in reverse, " R&D head Dr Gary Geaves told Electronics Weekly. "No energy by end of tube means no reflections."

And no, that was not a typo. £40,000 for speakers, and presumably there are customers out there...

Photographer triggers flashbacks

2008-06-19T12:47:41Z

Photography enthusiast Nick Pagazani was hindered by the range and fixed location of his camera's flash.

Since his camera has no connector for an external flash, he needed a light-activated slave trigger to fire a remote strobe. It had to ignore the pre-flashes used for red-eye correction and fire only on the main flash.

His solution: Use a microcontroller to count pulses from a phototransistor and trigger the strobe at a switch-selectable count. Brighten up your shadowy background with this flashy accessory.

You can download the build instructions in this zip file.

This Gadget Freak originally appeared in Design News.

Circuit Description

For the microcontroller I decided to use the PIC12F629 for its small size and the fact that it has an internal oscillator to help reduce the part count. The main portion of the circuit is the sensing circuit.

]]> Photography enthusiast Nick Pagazani was hindered by the range and fixed location of his camera's flash.

Since his camera has no connector for an external flash, he needed a light-activated slave trigger to fire a remote strobe. It had to ignore the pre-flashes used for red-eye correction and fire only on the main flash.

His solution: Use a microcontroller to count pulses from a phototransistor and trigger the strobe at a switch-selectable count. Brighten up your shadowy background with this flashy accessory.

You can download the build instructions in this zip file.

This Gadget Freak originally appeared in Design News.

Circuit Description

For the microcontroller I decided to use the PIC12F629 for its small size and the fact that it has an internal oscillator to help reduce the part count. The main portion of the circuit is the sensing circuit.

The phototransistor senses the ambient light and outputs a current based on the amount of light. Since we don't care whether it's light or dark, we use capacitor C2 to filter out that signal and only allow a sudden change in voltage to be passed. The capacitor and drain resistor were carefully chosen so that only a flash would create a voltage signal and not normal ambient light changes or fluorescent lights that flicker. This small flow in current opens transistor Q1 to put a "high" signal at GP0. This is the signal that tells the PIC that a flash has been sensed. The switch SW1 simply tells the PIC whether to trigger the flash output on the first flash, or the second.

The PIC triggers an SCR to fire the strobe. The SCR can block the high voltage and conduct the current surge required to fire a conventional strobe. It will also fire a strobe with a low-voltage trigger input without latching ON. For lowvoltage trigger inputs only, a second NPN transistor (I used a 2N2222) may be used instead of the SCR (See "alternative A" on the Schematic).

The connections at J1 connect to the external flash. For the flash, I use a standard hot-shoe mounted flash from my old 35mm SLR. I bought a hot-shoe adapter that allows the flash to mount to a tripod and has an external cable for connecting the flash to an external connector. I simply cut the connector off and connected the wires directly to the board.

Code Description

The code starts off by first setting up the usual parameters, one of which is the use of the internal clock, which helps make for a smaller layout. The main program begins at "main1" and starts by looking at the port GP0 and waiting for the line to go high. When it goes high, this means that the circuit has sensed a flash of light. The code then checks the state of SW1.

If it's open, then the next line executes and jumps to the flash routine to trigger the flash output. If the switch is closed, the code then checks to make sure that the input signal has gone back to 0, and then waits for the second flash signal to arrive.

The second flash signal is generally only a few milliseconds after the first, so the sensing circuit needs to dissipate the signal fairly quickly. Once the second flash signal is sensed, the flash is triggered and the program starts back at the "main1" loop.

Parts List

Amt	Part Description
1	PIC12F629 I/P microcontroller
2	0.1uF capacitor
2	1/4W 1 k Ohm resistor
1	1/4W 4.7 k Ohm resistor
3	1/4W 10 k Ohm resistor
1	1/4W 1 M Ohm resistor
1	2N2222 (or other) general-purpose transistor
2	SPST toggle switch
1	NTE5457 SCR (see schematic for alternate version)
Additional parts required
1 NTE3120 (or similar) Photo Transistor
1 3V Lithium Battery and holder
Nuts and washers for the toggle switches
Kaiser Flash Shoe Adapter, available at www.bhphotovideo.com
Photoflash Strobe
PIC development kit & software to program the PIC: K8048 (kit), Vm111 (assembled), available at www.apogeekits.com - requires RS232 port and cable. USB versions are also available.

This picture was taken with Nick's digital point & shoot and he says you can see that the flash triggered with perfect timing!

Winner announced - Gadget Freak's iPod shuffle compo

2008-06-18T12:09:17Z

Thanks again for all those who took part in this competition - we had more than 700 entries in the end - but there can only be one winner.

Cue drum roll and dimming of lights...

]]>

Thanks again for all those who took part in this competition - we had more than 700 entries in the end - but there can only be one winner.

Cue drum roll and dimming of lights...

Following a random selection, the winner of the iPod shuffle is one Eddie Harrison, Senior Marketing Engineer at Anritsu Ltd, in Stevenage! Congratulations Eddie, and happy listening.

Commiserations to everyone else, but better luck next time - we'll be kicking off the next Gadget Freak competition before too long.

(Suggestions for possible prizes would be welcome, btw - on an electronics theme preferably. I'm thinking about a solar power battery charger...)