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Problem with fluttering relay

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pmpm_sw

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This is about an IR controlled door opener.

The idea is that an IR signal activates a relay which in its turn set the voltage over the electronic lock to 0 -> door is open. I.e in idle mode, there is 12VAC over the electronic lock. -> door is locked

My problem is that he relay is fluttering. There are two cases:

1) In idle mode. I.e there are no IR signal
If I take away the voltage over the electronic lock, the relay stops fluttering and IR + relay works as intended.

2) If I activate a fluorescent lamp close by. During the lightening phase of the f-lamp, the relay flutters.
The IR sensor and the relay circuits are driven by a 4.5 v battery, so there should be no interference over the AC net.

Also tried to drive the electronic lock with 12VDC - same behavior

Any advice on this issue, would be highly appreciated.


Thanks,
 

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It is normal for a lamp to flicker on and off at double the mains frequency for long fluorescent tube lamps or at around 38kHz for compact fluorescent light bulbs.
You must smooth the on-off fluctuations from the IR detector with a filter.
 

Ok, so what would proper a filter look like in my circuit?
 

Are you aware that the relay is underrated for that voltage ?
In addition, the BC557 seems inverted in your drawing.
 

The IR sensor and 5V relay will not work for long from a 4.5V battery because their minimum allowed power supply voltage is 4.5V and a 4.5V battery quickly drops to below 3.6V. Use a 6V battery instead.
The BC557 is shown upside down in your schematic and its 1k resistor is not needed. I moved your 1uF capacitor and made it into a filter with an added 10k resistor.
The datasheet for the TSOP4838 shows that it needs a 4.7uF supply bypass capacitor and must have its IR modulated at 38kHz in bursts.
The schematic should be like this:
 

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If I take away the voltage over the electronic lock, the relay stops fluttering and IR + relay works as intended.

This suggests a poor power supply regulation. If you are using 3AA batteries, use C or D cells. Also twist the nicely the 5m connecting cable. Also cover the IR sensor with a IR transmitting visible blocking filter (most colored plastics will be ok; test with an IR LED and a digital camera).

The other problem should also go away if you nicely twist the 5m long cable (hopefully).
 

The TSOP4838 IR receiver IC already has a package that blocks ordinary light but passes IR.
What is "voltage over the electronic lock"? The relay coil voltage or the 12VAC voltage?
 

With "voltage over the electronic lock" I mean the 12VAC to drive the elecronic lock

btw: Thanks for the circuit proposal. I'll try it later today or tomorrow.
 

I think if the circuit is built on a solderless breadboard then the rows of contacts and the jumper wires all over the place will pickup interference from the 12VAC.
 

The IR sensor and 5V relay will not work for long from a 4.5V battery because their minimum allowed power supply voltage is 4.5V and a 4.5V battery quickly drops to below 3.6V. Use a 6V battery instead.
The BC557 is shown upside down in your schematic and its 1k resistor is not needed. I moved your 1uF capacitor and made it into a filter with an added 10k resistor.
The datasheet for the TSOP4838 shows that it needs a 4.7uF supply bypass capacitor and must have its IR modulated at 38kHz in bursts.
The schematic should be like this:

The 4.7 uF bypass capacitor applied to my original circuit removes the fluttering (both from the f-lamps and the electronic lock) - and it now works as intended.
Thanks for pointing me in the right direction
 

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