What is the maximum permissible supply voltage for the MK120 modules please? I need to use them in a car,so they could see up to 14 volts with the engine running. At the moment they’re regulated down to 9 volts but the relay I’m using struggles to pull in at that voltage.
Is it as simple as letting them see the full 14 volts or do I have to change resistor values?
Chris.
Has not been tried but should work fine. If necessary, add 1, 2 or 3 diodes in series to drop the voltage a little bit.
Thanks for the answer,but I’ve never heard of using series diodes to drop the voltage? So in your expert opinion running it at 14 volts will be fine,even over a long period of time?
Chris.
Theoretically, 14 volts should not be a problem.
However, as I’ve mentioned before, it has not been tested how the unit will behave in a car.
Adding series diodes is a very common and low-cost way to drop a supply voltage.
Each diode drops about 0.6V
So what symptoms would I see that would mean that it doesn’t like the higher supply voltage?
Chris.
It won’t work in a reliable way…
Ok thanks for the help,I’ll run it from a 12 volt regulator just in case.
Chris.
One last question,as it needs to operate over a very short range (3-4 inches) I need to reduce the sensititvity by only using one of the transmitter LEDs,can I just use the one or will I also need to replace it with a series resistor?
Chris.
No need to change the circuit.
So I can just have a single one in place of the two?
Chris.
Does not matter.
Probably the circuit will work fine with two leds.
Strange things are happening.
Had this module on long term bench test before putting it in my car just to make sure everythings good,it was but now it isn’t.Had it powered from a 12 volt bench power supply regulated down to 9 volts and it’s been fine giving it about ten minutes of continuous on/off use every day.Been fine for about 3 weeks or so,but now it’s suddenly only got a range of about an inch,whereas before it would work over several metres.Worked fine one day sitting on the bench in the warm and dry,and now suddenly this still sitting in the sameplace.
Checked everything visually and it all appears to be fine.It sort of works now but instead of the nice steady tone I ot before when you break the beam it pulses very quicly instead,any ideas please?
Chris.
Found out it seems to be the photo transistor after I went to Maplins today and bought another kit,I need another one anyway but wanted to try parts from the new kit and this was the first one I swapped over.
Soooo… is it important as to the spec of the device I replace it with,and if so where can I get one from that will work?
Chris/
Should work fine with a general purpose 940nm phototransistor.
Thank you,I’ll get my secretary to order me one.
Chris.
Only just got round to trying a new phototransistor,used one of these from Maplins and it’s even worse and only has a range of about 2 inches…
http://www.maplin.co.uk/module.aspx?moduleno=17936
Can you give me a specific part number please or give me any help to point me in the right direction?
Regards Chris.
First, try the kit as-is (original parts, setup as described in manual, no modifications).
Use 12VDC regulated power supply or two fresh 9V batteries.
If possible, post links to pics of both solder and component sides of PCB (please: sharp and hi-res pics).
This forum does not allow to add pics, so use a free picture base instead.
I have tried the kit as it is,in fact I now have two of them wired “as is”.If I swap the phototransistor from the known good working kit to the known not working very well kit,the fault travels with it.
They are both working from a decent bench 12 volt power supply and both are further protected by 7812 voltage regulators,so I can’t see how it can be anything else other than the phototransistor?
Chris.
In that case, it is clear that the phototransistor is at the cause of troubles.
It is a regular 940nm water-clear phototransistor.
Velleman part# L-53P3C
Thanks for that,but do you have an eqivalemt Maplin part number please as the last one I bought which I thought was a direct eqivalent wasn’t?
Chris.