PIR to trigger 555 timer
Hi
I want the PIR to trigger the input of a 555 timer to set of a relay. In the circuit below, a switch (S1) is used to trigger it.
How can I connect the PIR to this circuit to trigger the timer? (U1 is a 555 timer)
![relaytim.gif](http://www.aaroncake.net/circuits/relaytim.gif)
I have an appropriate voltage regulator (7805) going to the PIR.
Thanks.
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I want the PIR to trigger the input of a 555 timer to set of a relay. In the circuit below, a switch (S1) is used to trigger it.
How can I connect the PIR to this circuit to trigger the timer? (U1 is a 555 timer)
![relaytim.gif](http://www.aaroncake.net/circuits/relaytim.gif)
I have an appropriate voltage regulator (7805) going to the PIR.
Thanks.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Don't worry. Be happy
Comments
Thanks for the tip about voltage. I just ordered 3V SSR relays because of this, which I could have saved. But then again, now I have some SSR relays
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-Paul
Problem is, I get only 3.5V out from the T2 emitter.
(if I use 5V for the whole circuit, it works with a LED)
What could be the problem?
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Also, the 555's monostable output is active high. The transistor is effectively inverting the signal from the 555 and only tripping the relay while the timer isn't triggered.
T1 should be an NPN transistor with the emitter connected to ground. You currently have it as a PNP transistor.
I would seriously consider putting the 555 back on +12V and just using an NPN transistor in place of S1 in your original schematic.
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-Paul
Here is an updated schematic. Can you revisit and tell me again what's wrong?
Thanks a lot.
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-Paul
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be 0.7 volts below the base voltage. That's why you don't get more than
3.5 volts at T2 emitter.
You should change T2 so that the emitter is grounded and move the
relay coil and D2 to the collector of T2.
Delete D1 since it isn't necessary.
phil
I will post the complete project once I'm finished.
Thanks for all the help.
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The PIR sensor needs some time to settle, so in the beg. I thought it wasn't working, but after a while it works perfectly.
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