stridey

I have a timing device triggered by tapeswitches that I would like to make wireless.

At present the tapeswitch is run over by a skateboard at speed and it triggers a clock. A second tapeswitch stops the clock. This works perfectly, and is very similar to a barrel racing system used in rodeos.

I have bought a garage wireless remote and reciever and wired the remote to the tapeswitch by utilising the on/off button. Whilst this woks perfectly when I trigger the tape by my foot or by hand, when I roll a skateboard over the tape the remote triggers for a fraction of a second, which isnt enough to fire the remote off completely or long enough.

What I need to create is a 1 second pulse, tirggered by the tape and I have tried making a 1 second timer using an LM555. This I then connected to a 4N25 optocoupler. Trouble is that the output side of the opto seems to not like acting as a 9v switch, and also the LM555 will switch on for a second but not re-set ready for the next skaters run....

What I need is a simple way of triggering the remote with a long enough simulated button press....whilst taking into account that the input pulse generated by the skater is tiny.

Any ideas? Thanks, Michael

audioguru

You forgot to attach your schematic of the cirecuit you tried.

A 555 can make a 1 second output when it is triggered by a short duration pulse. It is a monostable timer circuit. Its output high voltage has a loss of about 1.5V.

A 4N25 opto-coupler can switch 9V if its LED current is high enough, its load current is low enough and it is a common-emitter circuit. an emitter follower circuit has a loss of about 0.8V in addition to the output voltage loss of the 555.

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Uncle $crooge

stridey

Edit: I got it to work.....simple case of a short circuit.....I used the circuits below BTW...

Here is the 555 circuit I used, using a 9v battery.


And here is what I used for a different application, using a the 4N25 on the outputs to trigger a revolveing light as an indicator, wheras in the newer application I want it to trigger the remote.

Hope that helps...

audioguru

Your circuit needs a supply bypass capacitor to keep the voltage from jumping all over the place.

It looks like you did not have a resistor in series with the LED in the opto-isolator so its LED burned out.
Then you added another LED that doesn't activate the photo-transistor inside the opto-isolator, then it also burned out. Maybe the output transistors of the 555 also burned out.

The transistor that drives the relay is probably destroyed by the hundreds of volts that are generated by the inductance of the relay coil when it turns off, because you forgot to use a clamp diode across the coil.

Your circuit does not have a latch so the revolving light would work only for 1 second anyway.

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Uncle $crooge

stridey

Thanks for your help.

Do you have any advise what value resistor I should use, also for the blocking diode.

I presume The diode goes parralell with the resistor code, but which direction should I place it? (Dont want to risk burning the opto out)

Again, appreciate the , much needed, advice.

stridey

Also. sorry, can you advise on the stabilising capacitor?

When I use the circuit as described for rotating the light ideally I'd like that circuit to last for 5 seconds 'open'. How would i do that, is it a case of changing a capacitor value?

The other use, namely latching for a second, works fine in test, but thanks for highlighting the issues I have with the circuit. I hope your tweaks will make it more reliable, long term.

audioguru

I don't know why you have two supply voltages.
I don't know why you are using an opto-isolator.
I don't know why you use a relay instead of a power transistor or Mosfet to drive the rotating light.

I added a 0.1uF supply bypass capacitor at the 555 and added a 100uF supply bypass capacitor for the entire circuit.

I connected the reset pin4 of the 555 to the positive supply.

I calculated 30mA through the LED in the opto-isolator then added a series 220 ohm current-limiting resistor.

I reduced the value of the resistor supplying base current to the 2N2222 to make sure it switches on very well.

Attached Images

revolving light.PNG (33.4 KB, 13 views)

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Uncle $crooge

stridey

I have tried that circuit today, but I cant seem to get it to work.

There is a voltage at the Opto when I trgger it, that reads for a second, but its not latching the relay on the other side at all.

I see you asked those three questions at the beggining of your answer, but can you suggest a bteer way for me please?

All I need is for the 555 to trigger a pulse to switch another circuit on for 1 second, or is there a way of outputting 9v from the 555 to power directly?

audioguru

The circuit is supposed to turn on the relay for only 1 second. It does not latch.
If the relay does not activate for 1 second then something is destroyed or connected backwards.

Your original schematic shows a missing current-limiting resistor in series with the LED in the opto. Then the LED is probably burned out.

If you tried the circuit without the diode then the high voltage probably destroyed the transistor and maybe also destroyed the opto.

If the diode is connected backwards then the transistor is probably destroyed.

Why do you want the revolving light to operate for only 1 second?

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Uncle $crooge