I have two kits and have had polarity confirmed by two other people. Both kits are in a constant alarm mode. I have done a test in a completely dark room, and have also placed electrical tape over the IR sensor. When power is applied the receiver goes into alram mode. A Velleman moderator (Dec 8, 2006) mentioned voltages to to checked, I have included them here.
T1 .3mV AC - No change in light IR or other wse is case on the IR receiver
Pin 1 3.4 VDC
Pin 9 3.4 VDC
Pin 14 3.4 VDC
I noted that the directions indicate the T2 collector as “T” and that “T” should be placed on the lower side (1 above) of the transistor loctation. But the “pictuer” in the directions and on the cover show it as the emitter in the lower position.
I pulled a data sheet for the BC547C and noted that the collector would be in the upper side of the transistor location. I made the swap (turned T2 around) on one of my boards, but am still having the same problems - a constant alarm, regardless of ambient light or IR Transmitter state.
I thought, that possibly, the LM324 could be bad, so I picked up a new one for a local supply house. This did not correct the problem either.
Any help would be approciated. I have 3 unopened kits, I am to use at a school event and don’t want to look the fool.
OK - Thank the EEs at A&H Technologies for this one.
I bought my boards in OCT 08. I don’t know if there was an updates or REVS to the transmitter trace board, when it may have occured or if I just received two bad boards.
Here’s what they (A&H) found:
My problem was not with the receiver, but the transmitter. A&H Tech found that the emitter of T3 is not tied to ground. This appears to be a issue through the use of SK1.
To check this out, use an ohm meter and measure the resistance between the - battery pad and the - SK1 NEG and GND tabs. A&H Tech found that SK1 ground and negative tabs were not tied together, which did not allow T3 to function.
OUR solution, since I didn’t want to use a AC power adaptor, was to place (solder) a wire jumper between SK1 gound tab and the SK2 negative terminal.
For clearity I will try to explain this a little better here:
With the IR emitters facing up and viewing the trace (solder) side of the PCB -
SK1 is located at the bottom-center of the PCB with 3 large tabs in the following layout
…1 – +
…2 ------ NEG
…3 – GND
The schematic has 2 and 3 tied together as part of SK1, through the plug (labeled SW), but without the plug inserted a battery would not supply a NEG to all the right points in the circuit.
THE FIX, to use a battery, solder a jumper between 2 and 3 (see above) of SK1 - this allows the battery to properly apply power to the circuit. BECAREFUL - do not solder to the positive of SK1 as this would short the battery and, well - that’s bad.
After the jumper was soldered in place; I tested the IR barrier in the lab under fluorescent and incandescent lighting, without mask either the tranmister LDs or the receiver IRD. I was able to get just shy on 3 meters.
It works fine when the DC connector is mounted but not used, as the connector is equipped with an internal ground switch. However, if you do not mount it then of course there is no ground switch, so the unit will not operate.
Hi, we are also having trouble with this kit. We made the recommended modification (jumping the neg. and ground on the smaller board – smaller board, right?) We still have the same problem: alarm is constantly on. We have looked at everything 3 times and are out of ideas. What else can we check? Is there an actual circuit diagram somewhere, so we can see what values should be at what devices? Seems like a cool project, and my son is into troubleshooting it, but we are STUMPED.
Thanks! Andy & TIm
Your answer is confusing. If you need help, please be as specific as possible.
You saw what ? The diagrams ?
You saw the IR leds flash ? In that case, the transmitter is working. Check receiver assembly. Mind the direction of the phototransistor. Make sure IC1 receives 9V between pin 4 and 11. Check solderings for forgotten/bad/loose/touching solderings.
Hi Vel417,
Sorry, that message was from Tim, the 4th grade engineer. He thought it was pretty cool to see the LEDs through the camera (so did I). They did light up, not “flash” as you described, but they seem to work correctly. The receiver seems OK too. We have 8.65v between pins 4 and 11 on the IC ( we assume 4 & 11 are the center pins on each side?) We did make the ground/switch/battery modification described above, but that was on the transmitter. We tried it on the receiver, just for kicks, with no effect. So what else could be wrong? We were careful with the IC, so it should be ok. Any more ideas? That painful buzzer is driving us nuts!
We’ve purchased 7 of the MK120 kits. My son built the first. The receiver alarm stays on. We’ve tried operating from both battery and external 9 volts. I checked his work and found nothing wrong. So I built the second kit. Neither transmitter will silence either receiver. There’s obviously a problem with the kit. More complete troubleshooting instructions would be appreciated.
This kit has many places where errors can be made but I really believe that there is a component(s) failure. I have assembled many other electronic kits and I usually get it right after some trouble shooting. In my case the PMK120T(ransmitter) doesn’t light up at all. The PMK120R(eceiver) likewise is dead. I traced voltage to all components and all is OK. Is there some sort of trouble shooting guide?
Most likely there are two problems, because the receiver should beep if the transmitter is covered or not working.
Transmitters: there ar few parts. Check transistors, check direction of leds, check resistor values.
Receiver: If you can link to SHARP and HI-RES pics of both solder and component side, we can take a look at your assembly.
Yes, I agree about the receiver. I don’t know what you mean by SHARP and HI_RES. If you are asking if I can send you some pictures of both sides of the PCB, Yes, that would be great. How do I upload pictures to you? If I click on “Img”, I get but that doesn’t tell me where or how to select pictures that are on my hard drive. Does “” represent my computer’s fully qualified path to the picture? and does the picture have to be img format?
You cannot upload pics, that’s why we mention ‘link to them’, e.g. using a free online picture base.
Make sure they are sharp and hi-res, so no cell-phone pics
