Gadget Freak

Back to the future

Sometimes the best way to take a step forward is to take a step back in time. So Andrew Smith designed a fully-functional toy oscilloscope, made out of parts he found in his junk box, such as the EF91, EF80 and EF184 valves. Using a DC-DC converter to power the old (but still working) 7cm CRT he discovered in his loft, Andrew housed it in the same wooden box as the rest of the circuitry. The whole system runs from a single regulated 12.6V DC supply, which can be derived from a “wall-wart” PSU. Doc Brown would be proud.

Return to Taking the Temperature

This link explains how to build your own DigiThermo to measure time and temperature.

An accurate PC thermometer you need all year round

Award-winning designer Alberto Ricci Bitti designed this simple microcontroller-free DS1621 PC thermometer that requires no calibration. It's so cheap and simple because all you need is the sensor IC, a voltage regulator and a handful of diodes and resistors. It can be plugged into any free serial port and the temperature is shown on the Windows taskbar. Lucky for us, Alberto's friends all asked for a PC thermometer of their very own, so he decided to release the build instructions into the wild. A cheap and simple PC thermometer? Now that's hot. Or should we say cool?

Now he’s got the power to cut lightning down to size

People have always been fascinated by the fury of the heavens. Electronics prodigy Richard Hodgkinson created a lightning distance timer so he would no longer have to manually calculate the approach or retreat of a thunderstorm. He recycled a 70 KHz crystal from an old device for the oscillator. “Let there be light,” he declared as two HP 45MGC670 surface mount LEDs were attached to allow him to see measurements in the dark. And his project wouldn’t be complete without two 1.5V AA cells which are the heart of his timer. Now his creation is alive, all he needs is a wicked thunderstorm.

While recently designing an automatic test station employing a microcontroller, I faced a nonstandard task: Detect the presence or the absence of output pulses in the DUT (device under test). You might think this task is easy to accomplish by connecting an LED to the DUT output. The blinking LED provides evidence of the pulse's presence. That approach would work if that test were the only one you needed to perform.

The Design Idea begins:

You can fulfil a requirement for sampling the difference of two signals in two classic ways. You can subtract the two input signals with an instrumentation amplifier whose output connects to an input of a classic sample-and-hold amplifier.

The novelty circuit in Figure 1 illustrates the extremely low gate-leakage current typical of modern power MOSFETs. You can find parts that, in a moderately dry environment, will hold their state for days at a time. In operation, if MOSFET Q1 is off, the load - perhaps a lamp or a buzzer - pulls Q1's drain to nearly the 12V-dc power-supply voltage. R2 charges C1 to practically the same voltage. 

Analogue applications, such as testing, calibration, and general system operation, often require a sine waveform of accurate amplitude and frequency, with low THD (total harmonic distortion). Some applications demand that the generator of such waveforms have the ability to accurately synchronize the output with an external timing signal.

TEC (thermoelectric-cooler) temperature-control systems often have limited stability. The causes of these limitations are the thermal properties of the system, not the performance of the control electronics. Real-world thermal-control systems incur nonzero thermal impedances in the heat-transfer paths between the TEC; the thermal load, which is the object of thermostasis; the temperature sensor - for example, a thermistor; and the ambient temperature.

The voltage at Point A pulls down to nearly 3.7V, which you determine by adding the forward voltage of the optoisolator's internal LED, the phototransistor's voltage, and the LED's voltage: 1.3+0.6+1.8V=3.7V. The green LED then turns off.