More push button bistables

Following my trials and tribulations with seemingly-easy problem, Mike M contacted me with some simpler ideas to the same end.

more-push-by-mike-thumb.jpg

The application demands that two selectable leds to replace one, with any added circuit drawing power from across the feed to the led.

Mike said:

No need for fancy ICs – the attached flip flop circuit using humble CMOS 4069 inverters has served me well since the 1970s working from 3-15V supplies.

I think I may originally have discovered it in Don Lancaster‘s CMOS Cookbook.

more-push-by-mike-web.jpgAny high input impedance inverters will do so why not use the mosfet led drivers themselves (Circuit 2) thus eliminating the IC ?
—————————–

Thanks Mike

I am suitably humbled, because circuit 2 is exactly the sort of thing that I tried, and failed, to come up with before I tried the D-type circuits.

Mike went on to point out that the diode clamps in my original circuit would stop the circuit 2 scheme from working unless low gate voltage mosfets could be found.

However, my clamps were there to prevent both leds from being off simultaneously should the CMOS hiccough – allowing the supply voltage to rise and blow up the power supply.

Mike’s circuit 2 looks a lot more robust and is going to hold at least one fet on all the time, so I think my diodes could go and a resistor could be added in parallel with each of the leds to increase gate drive.

There are a whole bunch of mono, bi and n-stables on this blog and they were mostly hyperlinked until some IT changes at EW disconnected them all. As I can’t face putting all the links back in the right places, here is a list instead. 

 

A 74HC74 hysteresis mystery
Hysteresis mystery solved, probably
Two leds for one
And now the pcb
Simple circuit selects LEDs? – a tri-stable
More push button bistables
A 74HC4060 monostable?
Thoughts on another EEVblog – a power on-off bistable


Comments

One comment

  1. I would describe the flip flop circuit that I recently posted as MML or Mickey Mouse Logic – a term perhaps not familiar to younger engineers ?
    Many years ago I read the truly wonderful ‘ Art of Electronics’ by Horowitz & Hill
    http://www.amazon.co.uk/Art-Electronics-Paul-Horowitz/dp/0521370957
    Within it describes how simple logic gates can be used to create flip flops, monostables and the like with the addition of just a few resistors, capacitors or diodes. This was often a life saver before the days of low cost microcontrollers often eliminating the need for an extra (costly) IC to carry out a particular function.
    For a brilliant description of these techniques see:
    http://www.musicfromouterspace.com/analogsynth/mmlogic.html
    The site name is more than worthy of its name and I can personally recommend building/buying their low cost Weird Sound Generator Synth (WSG) built with just a 4069 Inverter a few transistors and a 741 Op amp !
    Amazing fun and just what electronics was meant for !

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>