Review of a IR DSLR Remote project

[LogicalShrapnel]

Hello,

I have a fairly simple schematic I'd love for someone to look over.

I'm trying to build a version a IR DSLR Remote triggered by the 3.5 stereo jack of my phone. I got the original schematic from this site and have since been in contact with a user here named Misterbenn who has done a similar thing.

I've based my solution on a thread here at the forum but have had to make some alterations due to different parts and in pursuit of better range.

Here is the final(?) setup I'd like you to inspect and see if I've done anything wrong.
View attachment 66452

Thanks in advance! I apologize for any problems in advance since my electronics knowledge is fairly limited.

 

[alec_t]

The emitter of the top transistor and the input to the base resistor of the lower transistor are both shorted to ground

 

[picbits]

The IR LEDs appear to be the wrong way round .

 

[picbits]

Also your resistors should be around 40-47 ohms to limit the current to the LEDs to 100ma at 1.35 volts with a 6 volt supply. If you're only pulsing them with a low duty cycle you could get away with putting more current through but using your 4.7R resistors would burn them out in a flash if they were to be stuck on.

I've not looked into the input stage yet - just spotted those potential problems

 

[LogicalShrapnel]

The emitter of the top transistor and the input to the base resistor of the lower transistor are both shorted to ground

I'm not sure what you are referring to here?

The IR LEDs appear to be the wrong way round .

Sorry, got the direction wrong in the schematics, they are mounted correctly.

Also your resistors should be around 40-47 ohms to limit the current to the LEDs to 100ma at 1.35 volts with a 6 volt supply. If you're only pulsing them with a low duty cycle you could get away with putting more current through but using your 4.7R resistors would burn them out in a flash if they were to be stuck on.

Lowering the value of the resistors gave me much better distance. They will always be pulsed so there should be no risk of burning them out.

 

[alec_t]

I'm not sure what you are referring to here?

Sorry, I was referring to the two BC547B transistors.

They will always be pulsed so there should be no risk of burning them out

You cannot guarantee that an audio input signal will cause them to be pulsed fast enough to prevent burn-out with those 4.7 Ohm resistor values.

 

[Misterbenn]

Good to see you on the forum. And I'm glad to see that you understood my comments on your last circuit and created your own solution. This showed greater understanding than you give yourself credit for.

Alec_t is correct you are currently shorting out your battery, please remove the link between audio negative and battery negative. You should consider that the audio input is a floating voltage referenced to battery negativevia 2 series 300ohm resistors.

This circuit will give good range with 3v battery, you may burn LEDs if you continue with 6v. The fact that your current transistors are designed to drive 100mA may currently be saving your LEDs from burning.

 

[LogicalShrapnel]

I dismantled the circuitry on my board to clean it up a bit, now I can't get it working again... I'll have to get back to you all once I have it working the way it did so that I can try out your comments.

I thank you for your comments so far, it's comforting to know there is someone more knowledgeable looking over my shoulder now and then.

 

[alec_t]

Post deleted

 

[alec_t]

I've simulated the circuit operation in LTSpice. Depending on the amplitude of the audio signal the current which passes through the audio source can be greater than the total LED current! That's not good.

To drive each LED at 100mA each BC547 in turn would have a collector current of 300mA. The maximum specified collector current for a BC547 is only 100mA, so the transistor will probably burn out quickly. A higher rated one should be used.

If the (replacement for the) BC547 is turned fully on to pass a 300mA collector current it will need a base current of at least ~30mA. Can your audio source provide that?

Also, there will be severe cross-over distortion if you are trying to transmit audio via an IR link with this circuit.

 

[Misterbenn]

Again i must agree with Alec_t. From the original circuit i sent you the resitor values were 300ohms of the gate and base of the BC547 I suggest you change to this.

Alec_t this circuit is for an IR remote trigger for a DSLR camera from the audio output of a smart phone. The transistors implement some basic XOR logic from the 20kHz audio outputs to get 40kHz. If you look at my original thread you'll see my circuit which works really well!

 

[LogicalShrapnel]

Hi all, thank you for the valuable input!

I have removed the shorting of the transistors. The battery negative side is now only connected to the signal though the resistors.
I have replaced the BC560C transistors with 2N3906 transistors. They are marked at 200mA.
I tried replacing the 32 Ohm resistors with the original 330 Ohm but I lost about 2 meters of range by doing that.
I tried going down to 3V but that lost me about 2 meters in range as well.

My multimeter is slightly broken it seems. I can only get current readings on the 10A setting which makes it hard to measure current. But for voltage I get up to 0.06V when continuously triggering the signal and measuring over one of the LEDs which I interpret as being far from overloaded. Though it might be higher since it's pulsing and the multimeter might not catch the complete measurement (I'm guessing?) But why am I not getting a much higher value? 0.06V for a 1.35V LED seems like "nothing", or is it just the multimeter that is not catching the real value since I get almost 10 meters of range on it.

I'll be back tomorrow with some more exact distances with different setups.

 

[alec_t]

is it just the multimeter that is not catching the real value

Very likely. Most meters are sluggish and average the applied voltage. For brief pulses the average is low.

@Misterbenn
Scrub the bit about distortion. I forgot this was for DSLR control .

 

[LogicalShrapnel]

Alright.

I've tried going down to 3V, I've tried increasing the value of the 32 Ohm and 4,7 Ohm resistors respectively and I've tried going back to the BC560C transistors but whatever I change I loose a fair amount of distance. So it seems I've found my final setup.

I do value the comments and recommendations but since it seems to be working fine with this setup and gives me added range I don't really see why I should hold of on it. Besides, the parts are so cheap that if it breaks I can just build a new one

Thank you very much, I've learned a lot through this project and your comments!