Son of Operating a relay with a PIR sensor

Thread Starter

allenpitts

Joined Feb 26, 2011
166
Hello All About Circuits Form,
Have learned a lot about the PIR sensor/relay combination.
I have gone from

to


I have bread boarded this and done it on a PCB and it works great.
(Reload Ron lamented the demise of Radio Shack as a source for small
prototyping boards. Have found a supplier for the Archer 276-1591B at
http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-21-114-/21-4595
and board that in some ways is an improvement:
http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-21-117-/21-4610
)
Working on getting this PIR relay combination to work an LED display
http://www.vellemanusa.com/products/view/?id=351406
The schematic shows a momentary switch SW1:

It is a switch that connects two different traces at the same time. It seems they both must
be closed at exactly the same time because experimentation with using jumpers to close them resulted
unpredictable results.
So it was reasoned that a DPDT relay would get the job done.
Have tried two different DPDT relays:
CIT WJ0982Cs9VDC
and a
Kest KS2E-M-DC12
Here's the problem: Have breadboarded the PIR to Relay Schematic just like that shown herewith
above. I can get the either relay to work if I take out the LED and R1. But when I put the LED and the R1 the relay
won't close. The resistance of the relay was measured at about 130 ohms so it was tried with
100 ohms for R1. Same result. So it was tried with no R1 resistor between LED1 and Vcc. Still no relay
operation.
So it looks like the circuit will work with SPST relay but not a DPDT relay. That doesn't make sense.
What am I missing?

Thanks.

Allen in Dallas
 

Alec_t

Joined Sep 17, 2013
14,389
So it was tried with no R1 resistor between LED1 and Vcc. Still no relay operation.
Not surprising. The LED was severely reducing the voltage across the coil.
T1 is probably having difficulty providing enough current to drive both the relay and LED. Leave R1 at 220 Ohms, but try reducing the value of R2 to, say, 330 Ohms (providing that won't draw excessive current from the PIR output). What is the PIR output rating? What is the supply voltage?
 

Thread Starter

allenpitts

Joined Feb 26, 2011
166
Hello Forum,
Before any body spends too much time on this.
I found the mistake. It was in the breadboard
logic.

Allen in Dallas
 

Thread Starter

allenpitts

Joined Feb 26, 2011
166
Not surprising. The LED was severely reducing the voltage across the coil.
T1 is probably having difficulty providing enough current to drive both the relay and LED. Leave R1 at 220 Ohms, but try reducing the value of R2 to, say, 330 Ohms (providing that won't draw excessive current from the PIR output). What is the PIR output rating? What is the supply voltage?
 

Thread Starter

allenpitts

Joined Feb 26, 2011
166
Hello Alec_t,

Thanks for your reply.
I have got it to work.
But to answer your question.
The output of the PIR is 3.3v
The supply is a 9 volt battery.
The next step is to go from breadboard to PCB.
Then connect to the Velleman MK152
Will advise.

Thanks again

Allen in Dallas
 
Last edited:

JohnInTX

Joined Jun 26, 2012
4,787
FWIW Allen,
You can get proto boards like that and much more at Tanner's in Carrollton, TX. Valwood Pkwy a block west of I35.
Altex off Midway just south of Trinity Mills (near Addison airport) is a great source as well.
 

Thread Starter

allenpitts

Joined Feb 26, 2011
166
Hello Forum,

Before I went to PCB I decided to use the working breadboard of the PIR relay circuit, which
looks like Pencil's circuit above, to connect to and operate the LED display
http://www.vellemanusa.com/products/view/?id=351406

I hooked it up like this:


It worked, sort of. In this configuration the LEDs spin around
the wheel and stop when the signal from PIR stops. Always on
the same LED. In normal operate the wheel spins and then begins
to slow down until stops on a random LED.

So I played with it awhile and tried in several configurations
and finally hit on this which included reinserting the momentary
switch that came with LED display kit.


It worked!
Ok I just figured it out. I can move the bottom right SW1 connection
to P3 and the bottom left SW1 connection to P4 and eliminate the switch.
This is one of those cases where, by thinking logically about the thing
I didn't understand long enough to write it down and explain it
to some else, I figured out the answer.

So I didn't need DPDT after all. SPST throw will get it done.
Will PCB the PIR/relay circuit, hook it up to the LED
display and post a video of the whole thing in this thread.

I think I could have just used a transistor instead of a
relay.

Thanks.

Allen in Dallas
 
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