Rooting around in the fascinating stuff at the bottom of a draw labelled 'Engineering - Junk Miscellaneous'. Delving amongst the delightful...
More push button bistables
Following my trials and tribulations with seemingly-simple push button bistables, Mike M contacted me with some simpler ideas to the same end.
The application demands that two selectable leds to replace one, with any added circuit drawing power from across the driven led.
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.
Any high input impedance inverters will do so why not use the mosfet led drivers themselves (Circuit 2) thus eliminating the IC ?
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.
If you have comments, respond below, or to alice@electronicsweekly.
No email addresses are collected for marketing purposes from responses to this blog.
I will keep it that way for as long as possible.