Remote control receiver unit problem

[Roushon]

I built an amplifier with volume control a 64 step
attenuator.
The attenuator is controlled in binary operation by an IR
remote control receiver+logic circuit. The problem I am
having is that the receiver gets false signal whenever I
switch off a light in the room or change the
fan speed in the room by rotating the fan regulator.
I know fluorescent lamps emits IR light and
sometimes cause such problem, but do not understand
why the fan regulator or the switch cause this. The remote control
unit is powered by standard IE type transformer and
LM317 power supply. I am not attaching the circuit as
I think it is a common problem and should have an
easier solution. Kindly tell me what should I do?

Thanks and regards
Roushon.

[Mooly]

Could the problem be that a spike or interference is interfering with the logic rather than the IR section. Any interference to an IR receiver tends to just block it or make it appear less sensitive. It wouldn't cause it to output a code that the decoder recognised.

I suspect your problem is more fundamental, although just what is hard to say. Could be anything from a mains spike getting into the PSU to some weird form of EM coupling via nearby wiring.

[Roushon]

Thanks Mooly for your response. I will try using a spike
guard switch board. Or is it possible to add some kind
of small circuitry on the mains entry point of the amp
to avoid such spike interference? I think this will be a
better solution so that I can move the amp to some other
place without any bother about spike.

Regards
Roushon.

[Mooly]

You can add a mains filter but you really need to identify the problem first rather than guess. Could the supply be "dipping" in voltage as a load is switched on ? Maybe larger reservoir caps feeding the supply to the logic would help. Logic circuitry can usefully be decoupled with 0.1uf caps across the supply pins of IC's etc. However "switching off" a light points to a burst of RF energy caused by arcing contacts so a mains filter may help.

Filter vary in complexity, this is a bit extreme but it shows what is involved.

Audio Mains Filter DIY | DMS Audio

Identifying & Solving Mains Supply Problems

[janneman]

Originally Posted by Roushon

I built an amplifier with volume control a 64 step
attenuator.
The attenuator is controlled in binary operation by an IR
remote control receiver+logic circuit. The problem I am
having is that the receiver gets false signal whenever I
switch off a light in the room or change the
fan speed in the room by rotating the fan regulator.
I know fluorescent lamps emits IR light and
sometimes cause such problem, but do not understand
why the fan regulator or the switch cause this. The remote control
unit is powered by standard IE type transformer and
LM317 power supply. I am not attaching the circuit as
I think it is a common problem and should have an
easier solution. Kindly tell me what should I do?

Thanks and regards
Roushon.

What type of IR receiver do you use? If you use an integrated one, it's pretty impossible to get a false puls train that matches the code you are looking for. How do you decode the signal?

jan didden

[Roushon]

Thanks Mooly and Janneman. I should describe the circuit
a bit. The PS consists of:

12-0-12v 5Amp IE transformer, rectifier, 4700uF+4700uF+
0.1uF+2.2k 2W resistor and then LM317+1uF (tantulum)+0.1uF.

This PS before the LM317 also supplies some other
logic circuits and drives the relays (6) of the attenuator.

All the logic ICs are within 2 inches from LM317 so I did
not add any decoupling directly on the pin of the
IC.

The IR transmitter and receiver consists of the ICs HT12A
and HT12D respectively.

I will check the wiring again and place decoupling caps
directly on the pins of logic ICs.

It is true that the switches produces RF when putting Off
as it causes noise in the TV/Radio speakers. Also
I remember the old desktop computer I had before
used to shutdown in such interference.

Thanks for giving the filter circuit site. I will make it for
safety.

It seems to me there is severe problem in the wiring in
my apartment.

Regards
Roushon.

[Mooly]

Worth trying a mains filter I think. You can also suppress each switch with a snubber network. You can buy these ready made consisting of a 0.1uf cap and 100 ohm in series suitably rated for connection across the switch.
If you think the main wiring is dodgy then it's worth getting it checked out properly.

[godfrey]

I think the high frequency rejection of LM317 type regulators is not very good, so any fast spikes at the input go straight through to the output.

[janneman]

Think about it. What is the chance that a random spike causes exactly the right code to be output from the receiver/decoder?
The overwhelming possibility is that a spike causes your control systen *after* the receiver/decoder to react. Whether it has anything to do with the power supply is just a wild guess. (You can search for your keys under the streetlamp because there's light there, but if you lost them in another place it's pretty useless ).
So we really need a schematic to say anything intelligent about this.

jan didden

[Roushon]

Originally Posted by janneman

Think about it. What is the chance that a random spike causes exactly the right code to be output from the receiver/decoder?
The overwhelming possibility is that a spike causes your control systen *after* the receiver/decoder to react. Whether it has anything to do with the power supply is just a wild guess. (You can search for your keys under the streetlamp because there's light there, but if you lost them in another place it's pretty useless ).
So we really need a schematic to say anything intelligent about this.

jan didden

Hi Janneman,
Sorry for the weekend break! We know that the problem is with the
circuitry after the decoder. That is what we are trying to solve. There are several
logic circuits involved and the wiring in the amp cabinet is also under consideration.
The main receiver/decoder and the relay driver circuit is attached with its pcb design.
(The drawing is not very clean as I was only interested in making the pcb)
The circuit works very well except the occasional interference as I described above.
There is a recent modification to the attached circuit. I am not describing it in great
details as the problem was there before and after this modification.

Thanks and regards
Roushon.