Hello Forum,

Using this circuit to turn on an LED animation.

It was working yesterday. When I got home from work tonight
I started moving the PCBs into the implementation and it quit
working so noticed that the relay was not clicking even though
the LED was coming on. So I took the relay out to put in a new
one. When I got the relay out I tested it by touching the battery
terminals to the relay poles. The relay clicked and closed. So I figured
it was a cold solder. And put the relay back in. Stopped working
again. So I tried a new relay. Same result. So for some reason
the relay works when it is not in the circuit but does not work when
it has been solder into the PCB.
Any ideas?

Thanks

Allen in Dallas

PS This is a pictorial the PCB

 

Did you check the battery voltage when the relay is supposed to be energized?
9V batteries have a low capacity for driving a relatively high current load such as a relay coil.

 

Your relay contacts are shorting out the Base /Emitter of the transistor.

 

Your relay contacts are shorting out the Base /Emitter of the transistor.

Certainly looks like that. But you say that the relay closes and does not open.
What output voltage do you get out of the PIR module when nothing is detected? If it does not go below about 0.6V then the transistor may not switch off.
Try adding a resistor between the base and emitter. Another 470ohm should do. In fact, I would also try raising the value of the resistor from the PIR output to the base. A few thousand (k) ohm would be better. Try 2k2. Depends on the voltage out of the PIR module when something is detected.

 

Hello Forum,

Sorry if I was unclear.
The normally open pole does not close when the PIR biases the transistor when the relay is in the circuit
But when the relay is not in the circuit applying 9 volts to the relay closes the normally open poles.

Maybe I don't understand transistors. I thought a transistor is a just a switch and current only flowed from
the emitter to the collector. Is there current between the emitter and the base?

Allen in Dallas

 

.................
Maybe I don't understand transistors. I thought a transistor is a just a switch and current only flowed from
the emitter to the collector. Is there current between the emitter and the base?

Yes. A bipolar transistor requires a base current of at least 1/10 of the collector current to operate properly as a switch.

 

if you look at the points where the base and emitter are,they are connected to the relay contacts,which are shorting out the transistor, cut the track leading to the relay contacts and it should work.

 

Used as a switch, the base-emitter current should be about 10% of the load current, collector-emitter.

Gaaa, typed too slow.

 

Your relay coil is in series with the LED.

 

Hello Dodgy,
Will try that when I get home tonight.
But just to be clear. In the drawing marked 'PCB Relay w PIR' above
Is the emitter the pin coming from the PN2222 that is above the middle pin transistor?
or
Is the emitter the pin coming from the PN2222 that is below the middle pin transistor?

Thanks

Allen in Dallas

 

below to the batt neg.

Also as Alec-t said, the led is in series with the relay coil, and should be in parallel via the resistor.

 

below to the batt neg.

Also as Alec-t said, the led is in series with the relay coil, and should be in parallel via the resistor.

Hello AAC forum,

Thanks to Dodgy Dave, Alec T, Reload Ron, JDT Crutchow, et al. for your help.
I finally got it to work. Based on the input from Dodgy Dave and Alec T
the PCB circuit was reworked:

The PCB and the Velleman MK152 then went into a wheel.

About half way thru the clip the already unsteady camera work gets
even jumpier because I wave my hand to retrigger the PIR.

Thanks again.

Allen in Dallas