I'm using a wireless RC device the will wait forever for a signal, but once it receives that signal it goes to power saving sleep mode after 5 minutes. It can be reactivated by pressing a button on the device, but I can't manually go do that. I need a circuit to effect that button closure about 1 sec after the device is activated. Once it's pushed, it will wait forever again for the next signal. I can do that with a 4N25 but I can't do it as soon as the device gets it's signal, I have to wait at least a second or two before I do that button short , or any time before it falls to sleep in 5 minutes. I need the simplest, smallest circuit, with the fewest, smallest components. Space inside this thing is very, very, limited . . . as is my knowledge. Any ideas?

 

What would happen if you just kept pressing the button every now and then?

Say...every 4 minutes.

 

Using the 4N25 this is the simplest I can think of. Worth a try?
SG

 

What would generate "RC Device" signal, and how long will it last?

 

What would generate "RC Device" signal, and how long will it last?

Good question. The TS did state he could do that with a 4N25 but needed a delay. I guess he has that part figured out.
SG

 

For someone who needs a circuit, your question is missing a lot of information.

Sounds like you want a circuit that can detect/sense/interface with/whatever something from the RC device when it receives its signal, one timer circuit that is the delay, and one timer circuit that is triggered at the end of the delay and activates the optocoupler briefly.

If that is correct, then an 6-pin PIC in an SO package is the smallest thing I can think of. It has an onboard clock, is very low power, and can drive the opto directly. 1 PIC, 1 decoupling cap, 1 resistor, 1 opto.

With conventional timing circuits, time = capacitor size. This could be a CMOS 555 with a boxcar circuit on the output. Micrel makes a 555 derivative in an SO23-5. What is the shortest possible delay, and what is the shortest possible opto activation time?

AND

For either approach, what is the signal that will start the sequence? AC, DC, volts, frequency, source impedance - anything?

ak

 

I'm using a wireless RC device the will wait forever for a signal, but once it receives that signal it goes to power saving sleep mode after 5 minutes. It can be reactivated by pressing a button on the device, but I can't manually go do that. I need a circuit to effect that button closure about 1 sec after the device is activated. Once it's pushed, it will wait forever again for the next signal. I can do that with a 4N25 but I can't do it as soon as the device gets it's signal, I have to wait at least a second or two before I do that button short , or any time before it falls to sleep in 5 minutes. I need the simplest, smallest circuit, with the fewest, smallest components. Space inside this thing is very, very, limited . . . as is my knowledge. Any ideas?

Keypads are often strobed row/column layout, one set of connections pulses a group of button contacts, those are crossed by sense lines that are "watched" for activation. Its polarity sensitive, so you have a 50% chance of wiring the opto output correctly first time. There are AC output MOSFET optos that nearly halve the time spent on trial & error.

 

Below is the LTspice simulation of a two 555 timer circuit that, I think, provides the delayed signal you want.
It generates a pulse (Out2) about 2.4s after the falling edge of the input pulse.

 

Keypads are often strobed row/column layout, one set of connections pulses a group of button contacts, those are crossed by sense lines that are "watched" for activation. Its polarity sensitive, so you have a 50% chance of wiring the opto output correctly first time. There are AC output MOSFET optos that nearly halve the time spent on trial & error.

I agree. I have used the PVT312 for this kind of application.


edit: Added data sheet.

 

For someone who needs a circuit, your question is missing a lot of information.

Sounds like you want a circuit that can detect/sense/interface with/whatever something from the RC device when it receives its signal, one timer circuit that is the delay, and one timer circuit that is triggered at the end of the delay and activates the optocoupler briefly.

If that is correct, then an 6-pin PIC in an SO package is the smallest thing I can think of. It has an onboard clock, is very low power, and can drive the opto directly. 1 PIC, 1 decoupling cap, 1 resistor, 1 opto.

With conventional timing circuits, time = capacitor size. This could be a CMOS 555 with a boxcar circuit on the output. Micrel makes a 555 derivative in an SO23-5. What is the shortest possible delay, and what is the shortest possible opto activation time?

AND

For either approach, what is the signal that will start the sequence? AC, DC, volts, frequency, source impedance - anything?

ak

 

Trigger for this thing is a short 9V pulse. I found the attached device that I think gets me close. I don't know what it is, but I have it working. It turns the LED on with an input pulse and turns it off after about 5 seconds. It is certainly small enough, even with the support components. I assume I don't need the LED, just the signal line for it. What I can't get past is how to use the event of that LED line going low to short a microswitch, either directly or through a 4N25 and then release it. I guess overall, what I need is just a circuit to take a button push (got it), delay a short period (got it), and then simulate a second button push (still looking for this one). I'm hoping it may be just some combination of logic gates and inverters or some combination of transistors & gates. At 67 & with no background in electronics it's just coming real slow. Thanks to all for your suggestions but you just know how limited my space is.

 

Trigger for this thing is a short 9V pulse.

what I need is just a circuit to take a button push

Still confused. I have your circuit ready to post, but I can't without some more clarity.

1. Is the thing that triggers the delay circuit a 9 V positive-going pulse or the closure of switch contacts?

2. What is the power supply voltage for the delay circuit?

3. How wide (number of seconds or milliseconds) is the "9V pulse"?

ak

 

Well...thanks for answering my first question in this thread.

My idea was...

If pressing that button every 4 minutes didn't cause any problems with normal operation, then you could use a simple 555 to drive the 4N25.

Since you have 5 minutes to press the button before it goes into sleep, pressing the button every 4 minutes will allow you to miss that critical few seconds from the signal and still reset the system in time.

No need to interface with that 9volt pulse, just power the module (555 & 4N25) and bypass the "button".

Of course this wont work if pressing the "button" without receiving "the signal" will disturb normal operation.


Also if “pressing the button” can be done by simply grounding one of the pins, you could eliminate having to use the 2N25, by using the discharge pin on the 555. (it requires a clever rewiring of the 555)