Would it be possible to get the capacitor to start charging only when the slide switch is 0V?

Take R1 to one of the points whose potential is impacted by the switch's position.

 

The schematic is a little convoluted and can be simplified.

 

goo

Connect R1 to the output of the inverter Ic6a instead of pin 8, and put a diode across it Cathode to the inverter,then when the switch is in the negative position the inverter will go high and charge the capacitor, the capacitor will discharge only when the inverter goes low via the diode.

Edit you can do away with the inverter and the OR gate, replace them with a cd4093 gate instead.

Thanks for the reply: although as the diode's cathode facing the output of the inverter, the time it takes for the capacitor to charge is very slow - so I'm probably not going to include it.

 

If the capacitor is taking too long, lower the resistor to suit your time, try 330k. The diode is to discharge it fast.

 

How can I make a logic gate output of an and gate only last for a few seconds?

 

Your push button when pushed is directly shorting your +5v to 0V. And it is also applying +5V to the output of your 555. It would be bad for the 555 chip.

The center of your slide switch is connected to 0V and should be removed.

Allen

Looks like you are off to a good start. Yes, the RC on the Reset of the 555 should give you that initial delay you wanted. If you want to manually increment / decrement as well capacitor couple the clocks. The AND gate in another drawing gives you the wrong clock polarity. The CD4510 counts on the rising edge of the clock pulse.

 

If the capacitor is taking too long, lower the resistor to suit your time, try 330k. The diode is to discharge it fast.

Even if I lower the value of the resistor to 10K the charging time is severely increased. How could I adapt the circuit - so the capacitor charges after 60s and it discharges very quickly when the slide switch is high?

 

Post your circuit so we can see what you need, as i said earlier put a diode across the resistor Cathode to positive supply.

 

Post your circuit so we can see what you need, as i said earlier put a diode across the resistor Cathode to positive supply.

How do I get the capacitor to discharge immediately or very quickly? Is this possible?

 

D1 is wrong, it needs to go across R1 with Anode to C3, the Cathode to ic6. If its taking too long to charge up, reduce R1 to 330k.

 

D1 is wrong, it needs to go across R1 with Anode to C3, the Cathode to ic6. If its taking too long to charge up, reduce R1 to 330k.

Like this?

 

D1 is wrong, it needs to go across R1 with Anode to C3, the Cathode to ic6. If its taking too long to charge up, reduce R1 to 330k.

Thanks for the help!

 

When I run the schematic in a simulator, everything works fine. When I build the circuit on a breadboard, after the delay has finished and the RESET is high, the number jumps. It's usually to 8 but sometimes other numbers. What's going on, is this because of interference. I tried out the Astable on the clocks of 2 BCD counters. The same problem persists - something's wrong with the Astable.

 

I've tried replacing the resistors and capacitors, even when I change the delay time to a large number: when the capacitor has fully charged, and pin 4 is high, the number changes to 8 (for example) and then counts down as normal.

 

If it works in software, then your pcb or breadboard wiring is faulty, suggest you recheck your work, or post pictures of your built work,and circuit diagram maybe we can spot a problem.

 

Changing the state of pin 4 seems to affect the numbers. Do you know of what could be the problem?

 

After doing some testing, the slide switch itself seems to be the problem. When I used a push switch connected to the reset pin - everything works. I need to be able to latch each state of the slide switch

 

Another thing: when I move the slide switch really quickly between the two states, the numbers don't jump. However, if I move the slide switch slowly the numbers begin to jump. I need some sort of latch.

 

I've found the problem: the RC network that delays the Astable. I debounced the slide switch using a schmitt invertor. When I connected the output of the schmitt invertor (slide switch) to pin 4 directly I have no problems. But when I connect pin 4 to the RC network to delay the astable the number jumps. What is going on?

 

I've found the problem: the RC network that delays the Astable. I debounced the slide switch using a schmitt invertor. When I connected the output of the schmitt invertor (slide switch) to pin 4 directly I have no problems. But when I connect pin 4 to the RC network to delay the astable the number jumps. What is going on?

Maybe try going slide switch -> rc circuit (time delay, but also a form of debounce) -> schmitt inverter.

My thinking, which is just a guess, is that when you connect the rc network to pin 4, the voltage climbs and drops gradually through the threshold voltage for pin 4, and that maybe bad things are happening when you've got pin 4 too close to the threshold voltage. The schmitt inverter would make sure pin 4 always sees a distinct, clear state of either high or low, never in between.

My knowledge of the inner workings of 555s is very weak, so I could be way off base about the nature of pin 4's responses.