Been working on this for a while. Circuits are not my strong point. Power Source =5.5v dc The first image is a 4093 NAND that another used helped me with. It changes a dual led from one color to the other and sounds the buzzer for 750ms each time the 5v touch pad is pressed. The second image is the 5v relay and an NE555. This circuit will engage the coils relay and hold it until C1 discharges. What am I saying. You guys know this stuff. Let me get to the problem I'm having. Well it's more of a concern. I've connected pin2 from the output of the touch pad and pin4 from the output of the gate (where it connects to the buzzer) when the touch pads trigger goes high it causes pin4 to go high. At the same time the output of the gate goes low sounding the buzzer and pin2 also goes low which triggers and starts the 555. In theory it works but my concern is that the two pins may trigger at the same time causing unpredictable results. My question is can pin4 be delayed? Perhaps with a simple resistor? I've tried to figure this out but not having any luck. I do thank you in advance for your help
Well technically you can use an RC circuit to create a delay to when pin 2 is triggered but a better answer (I believe) is this after a little information: For the 555 timer to work properly, in either astable or monostable mode, pin 4 must be connected to positive voltage (at least 0.7 V according to Datasheet) prior to any input trigger voltage. This is because this reset pin works to disable the 555 timer when it’s held low. So a problem could arise if pin 4 (reset) is made high and pin 2 is made low at same time. To solve this problem, you’ll want to attached pin 4 to positive supply, and just use the pin 2 trigger as you were. When the pin 2 is high, your relay will be off, and only when pin 2 is triggered low, will the relay be on for the brief period determined by RC circuit attached to 555 timer.
Also if you want to really want to give your piezo buzzer a 750ms on time, then you should consider removing the R1 and C1 connected to the nand gate. Instead connect the output of touch sensor to nand gate (connected as NOT gate like you have) then connect the output of that nand gate to pin 2 of a second 555 timer which is configured in monostable mode with RC network to give a 750ms period. Hope this helps.
I’m just going to explain using another answer post.
Ok this clarifies things. So I’ll have to tell you that from my knowledge of the 555 timer and from the Datasheet they indicate proper use of 555 timer in monostable mode when the trigger pin is only triggered momentarily and not latched. Actually when it’s latched to a low voltage I’m not entirely sure what happens. It may latch the output and not work like desired.
So the circuit involving the LED, NAND gates, and the RC circuit with piezo would work as planned since you indicated that your sensor latched it’s output. However as stated above, I can’t guarantee the relay circuit to work even with my modification. I believe a better option here would be to use an arduino or some other microcontroller that would turn be able to turn on the relay and piezo buzzer for desired time when one of the pins is rising edge triggered. Your led circuit can remain though. And you would have to interface transistors with microcontroller to turn on both the buzzer and relay.
It seems there is a limitation of this 555 timer to your application.