Hi fellas
I'm trying to change this circuit to detect IR and get a 3v3 at output(instead of the LED) to connect it to my MCU:

My circuit is like this but it doesn't has 1k resistor(What's the usage of this resistor?) and supply is 7.5v DC and transistor is bc547. for LED I use a red LED and 320ohm resis' instead of 100ohm resis'. I used a pot to change the voltage that the IR sensor(diode) draw. this was just for a test (I know it's not wisely). when I turn on the circuit and decrease the pot, it makes smoke! why?

And also any seggestion for improve the circuit?

 

If the 1K resistor is changed to zero, you have no linear current limiters. Add 100 ohms in series so it is impossible to adjust to zero ohms.

 

What #12 said. I don't clearly get it either, so could you draw a schematic showing EXACTLY what you have wired up?

 

What #12 said. I don't clearly get it either...

Like me.

...so could you draw a schematic showing EXACTLY what you have wired up?

Wasn't my explanation enough clear? ok, let me take a photo of my circuit. there you go:

 

#12 covered the smoke. This is your circuit as it appears on the Internet. Since you mention 3.3 volts possibly the circuit will be used to drive a uC (micro-controller). The circuit itself is rather basic and if you want a 3.3 volt output from an IR detector using an IR diode theink about using a circuit like these types. Your pot is smoking because with nothing to limit current as the R value is decreased the I value increases till something has to give so the pot sees excessive current and burns up.

Ron

 

No your explanation was not clear enough (where did you connect the pot?) and the picture does not show that either.
Please post a schematic.

 

...To avoid future agro, better toss the (now) damaged potentiometer...

TTFN
HP

 

Thanks Ron for perfect answer.

No your explanation was not clear enough (where did you connect the pot?) and the picture does not show that either.
Please post a schematic.

Ok,

 

... Since you mention 3.3 volts possibly the circuit will be used to drive a uC (micro-controller). The circuit itself is rather basic and if you want a 3.3 volt output from an IR detector using an IR diode theink about using a circuit like these types.

I just have IR sensor (I do not have phototransistor in stock).

 

Where does the ground go to?

If it goes to the negative of the 7.5V then there is one source of smoke: you have a fixed voltage across a small to zero resistance.

Please don't make us guess any further as to your intent. Make a full and complete schematic.

 

I just have IR sensor (I do not have phototransistor in stock).

Well if you have a link to your sensor data sheet things might go much better.

Ron

 

Where does the ground go to?

If it goes to the negative of the 7.5V then there is one source of smoke: you have a fixed voltage across a small to zero resistance.

Please don't make us guess any further as to your intent. Make a full and complete schematic.

Ops , sorry. yes, it goes to the negative of the 7.5V.

Well if you have a link to your sensor data sheet things might go much better.

Ron

Unfortunately the vendor that I have purchased this sensor from doesn't provide any datasheet for this diode.

 

If your sensor is a photodiode you may not get enough transistor base current to drive a LED properly. But if you just want to provide a signal to a micro you could try this arrangement :-

R1 is a pull-down resistor to reduce the chance of spurious noise turning Q1 on. R2 and R3 form a voltage divider to ensure no more than ~3V gets to the micro input (assuming the micro has a 3.3V supply).

 

If your sensor is a photodiode you may not get enough transistor base current to drive a LED properly. But if you just want to provide a signal to a micro you could try this arrangement :-
View attachment 87225
R1 is a pull-down resistor to reduce the chance of spurious noise turning Q1 on. R2 and R3 form a voltage divider to ensure no more than ~3V gets to the micro input (assuming the micro has a 3.3V supply).

Thank you but that Ground symbol confused me (below R1). for what is that?

 

Thank you but that Ground symbol confused me (below R1). for what is that?

It merely indicates connection to the 'common return' --- For the purposes at hand you may ignore it

Alternatively, you may 'erase' the horizontal line at the bottom of the diagram and similarly draft the 'lower end' of R3 and the negative line from V1...

TTFN
HP

 

If your sensor is a photodiode you may not get enough transistor base current to drive a LED properly. But if you just want to provide a signal to a micro you could try this arrangement :-
View attachment 87225
R1 is a pull-down resistor to reduce the chance of spurious noise turning Q1 on. R2 and R3 form a voltage divider to ensure no more than ~3V gets to the micro input (assuming the micro has a 3.3V supply).

Thanks a lot for schematic.
I wired up it and now it's working very well.
Thank you Hypatia's Protege for reply.