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# IR-controlled, 5V output switch circuit question

#### lb483

##### New Member
I'm looking to create an IR-controlled, 5V output switch for some battery-powered candles that are a pain to keep manually switching on and off. I found the following circuit online which appeared to provide what I'm looking for:

As I'm not powering a 230V load, I've excluded the relay and just taken the output across the diode. However, it doesn't appear to work for me. Sometimes I get 5V across the diode and it ceases when the 1738 receives an IR signal. At other times I get 5V that won't stop or 0V that wont start.

Can someone advise what I've done wrong? Have I misinterpreted the function of this circuit for my use case or have I just constructed it incorrectly?

Thanks.

#### Les Jones

##### Well-Known Member
How is the transmitter signal encoded ? Most TSOP detectors only respond to signals that conform with that used by TV remote controls. Look at the datasheet for your TSOP1738.

Les.

#### Nigel Goodwin

##### Super Moderator
It's an utterly crap circuit - it's never going to work acceptably - one of many such available on-line. It's also missing the important decoupling capacitor across the TSOP - adding a 47uF there 'might' improve things a little?

You really want a proper encoded transmitter (some kind of IR remote, such as a TV one), and a suitable decoder - a PIC or similar programmed to do the job.

#### lb483

##### New Member
How is the transmitter signal encoded ? Most TSOP detectors only respond to signals that conform with that used by TV remote controls. Look at the datasheet for your TSOP1738.

Les.
Supposedly, it's just supposed to detect the IR from a TV remote and react accordingly. That's what I'm using but without success.

#### lb483

##### New Member
It's an utterly crap circuit - it's never going to work acceptably - one of many such available on-line. It's also missing the important decoupling capacitor across the TSOP - adding a 47uF there 'might' improve things a little?

You really want a proper encoded transmitter (some kind of IR remote, such as a TV one), and a suitable decoder - a PIC or similar programmed to do the job.
Thanks for the info; glad I didn't put too much effort into it :-/ I'll do some searching for what you've suggested.

I didn't expect it to require anything complex given the range of cheap (and cheap looking), remote controlled candles available. I thought I could just implement something similar into the power line of the nice-looking battery candles we have.

#### Nigel Goodwin

##### Super Moderator
Thanks for the info; glad I didn't put too much effort into it :-/ I'll do some searching for what you've suggested.

I didn't expect it to require anything complex given the range of cheap (and cheap looking), remote controlled candles available. I thought I could just implement something similar into the power line of the nice-looking battery candles we have.
The circuit you posted above is considerably more complicated then using a processor, and takes a lot more physical room (as it uses a 16 pin chip and many extra components).

Small NEC IR remotes are available for hardly any money at all, and can be decoded with a PIC etc.

For your circuit above, the TSOP, R5, a 47uF across the TSOP, an 8 pin PIC, R3, and T2 are all that's required.

#### lb483

##### New Member
The circuit you posted above is considerably more complicated then using a processor, and takes a lot more physical room (as it uses a 16 pin chip and many extra components).

Small NEC IR remotes are available for hardly any money at all, and can be decoded with a PIC etc.

For your circuit above, the TSOP, R5, a 47uF across the TSOP, an 8 pin PIC, R3, and T2 are all that's required.
Thanks again. Having never used a PIC, I'm presuming some programming is going to be required. I'll have to do some investigation into this solution but I'm sure you're right about the simplicity.

#### AnalogKid

##### Well-Known Member
It sounds like you want the output to be activated when the remote button is pressed, stay activated when the button is released, and be de-activated when the button is pressed again.

Correct?

If so, then your circuit will not work. the output of the remote is a digital bit pattern modulated on the IR light. The output of the 1738 is a recreation of the input digital pattern. T1, C2, and R1 act as an AM detector, to turn the demodulated data burst into an envelope waveform that acts as a single clock pulse for the 4017. A possible problem is that the filter values for C2 and R1 are not correct for the pulse, and ripple in the output waveform is being seen as multiple clock edges.

BUT with no component values, it is impossible to say.

Also, the 4017 outputs cannot source much current. Depending on the values of R2 and R4, the LEDs might be overloading the output stages.

ak

#### lb483

##### New Member
It sounds like you want the output to be activated when the remote button is pressed, stay activated when the button is released, and be de-activated when the button is pressed again.

Correct?

If so, then your circuit will not work. the output of the remote is a digital bit pattern modulated on the IR light. The output of the 1738 is a recreation of the input digital pattern. T1, C2, and R1 act as an AM detector, to turn the demodulated data burst into an envelope waveform that acts as a single clock pulse for the 4017. A possible problem is that the filter values for C2 and R1 are not correct for the pulse, and ripple in the output waveform is being seen as multiple clock edges.

BUT with no component values, it is impossible to say.

Also, the 4017 outputs cannot source much current. Depending on the values of R2 and R4, the LEDs might be overloading the output stages.

ak
You're correct about the functionality I was looking to achieve. I've excluded the LEDs since the circuit is to power a bulb and they'd be redundant for telling me whether the circuit was on or off.

Re: the component values:
R1 = 220K
R2 = 330R (UNUSED)
R3 = 1K
R4 = 330R (UNUSED)
R5 = 47R
C1 = 100uF-16V
C2 = 100nF-63V
C3 = 470uF-16V
D1 = 1N4007
D2 = Red LED (UNUSED)
D3 = Green LED (UNUSED)
Q1 = BC558
Q2 = BC548
IR = TSOP1738
IC1 = CD4017
RL1 = Relay 5V DC (UNUSED)

#### Nigel Goodwin

##### Super Moderator
Well looking at the component values, C1 (at 100uF) looks like it's the missing capacitor off pin 2 of the TSOP, so probably has been drawn wrongly connected on the diagram?.

##### Well-Known Member
Wow, then go to Aliexpress. Looks like there are tons for 60 cents (
£5 =~ $6 = 10 relays + remotes) and shipping is how much...... Regards, Dana. #### Nigel Goodwin ##### Super Moderator Most Helpful Member Wow, then go to Aliexpress. Looks like there are tons for 60 cents ( £5 =~$6 = 10 relays + remotes) and shipping is how much......

When I had six (3 black, 3 white) a couple of months ago, they were £0.22 each, £2.32 postage, £0.73 VAT, for a total of £4.34

I use both AliExpress and Banggood, and it's a good idea to check the relative prices - as either can be cheaper.

#### shokjok

##### Member
Correct me if I'm wrong, but T1 should be a UJT to generate the pulses needed by the CD4017, which can be subbed with a 4013 and eliminates T1 for this circuit.

#### Nigel Goodwin

##### Super Moderator
Correct me if I'm wrong, but T1 should be a UJT to generate the pulses needed by the CD4017, which can be subbed with a 4013 and eliminates T1 for this circuit.

Sorry, but you are completely wrong - T1 is exactly what it needs to be - it doesn't generate pulses, it inverts them. The pulses come from the IR modulation from the TSOP IR receiver chip.

A UJT would be completely useless, and prevent the circuit from working at all.

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