Desperate help needed with counter circuit!!!!!

[manghameister]

First of all I would like to say that I am a complete electronics newbie, I literally know nothing so any advice is going to have to be simple and step by step.

Here's the situation, i'm trying to design a battery powered counter that uses three seven segment displays. I'm using a very basic simulator program called crocodile clips so apologies for the quality. There are only two switches that are really important in my design. In the top left is the on/off switch, and on the right of the second seven segment is the switch that will increase the displayed value by one. However when I turn the circuit off and then on again the decoders and counters break. I believe that i may need some sort of voltage regulator, if so can somebody please show me exactly what i should do, if not any other suggestion would be welcome

 

[ccurtis]

Of course, you should regulate with the HC series, but you might try switching the high side (plus side of battery) instead of the low side, first. Maybe that's the problem. There may be ground bounce causing reverse voltage condition if you switch the circuit off then immediately on again.

 

[manghameister]

here is a pic of the circuit when the problem occurs, the blanked out components are the ones which break. If I do need a voltage regulator can you show me exactly where as I just checked the program and it doesn't have one.

 

[ericgibbs]

here is a pic of the circuit when the problem occurs, the blanked out components are the ones which break. If I do need a voltage regulator can you show me exactly where as I just checked the program and it doesn't have one.

For the simulation, you could connect two diodes in series with +V terminal of the battery.

So the battery +V to the anode of a diode, another diode then the +V to the logic supply.

Each diode will drop about 0.65V, so 2 * 0.65V = 1.3V drop, this will leave about +4.7V at the logic power pins.

OK.?

 

[manghameister]

I have tried what you suggested and have discovered a new problem. I can lower the voltage sufficiently so that the decoders and counters do not break, however the 7 segments then turn off!

 

[ericgibbs]

I have tried what you suggested and have discovered a new problem. I can lower the voltage sufficiently so that the decoders and counters do not break, however the 7 segments then turn off!

hi,
Looking at the circuit, in a 'real' circuit the 7segs would work OK.

The problem is in the simulator.

Try using just one diode, not two.