# IR receiver giving constant current

simulate this circuit – Schematic created using CircuitLab

This is a circuit I made with an 1838D IR receiver in order to test if a tv remote is working, but as soon as I press the button, the led faintly lights up, and when I use a remote at the receiver, it just starts blinking. I tried using the transistor you see in the picture in order to make the LED supposedly light up stronger, but because of that constant flow of current out of the receiver, the transistor’s base turns the emitter on, and the LED still faintly lights up, as if there was no transistor.

Is there a way to fix that constant flow of current from the receiver, or is that something receivers are supposed to do?

• Diagram 3 of the datasheet shows you need a pullup resistor from the output pin to Vcc of 20k or more. Diagram 6 shows that the output is HIGH when no IR is sensed and LOW when there is IR. This should be enough information to be able to adjust your circuit to work properly. – CharlieHanson Jan 6 at 13:24
• Sorry about the dumb questions, but wich datasheet did you see and what is a pullup resistor? – Jasonikakis Jan 6 at 13:27
• and something else: i think i might be exaggerating, but I have a 91K resistor. Will that do it? – Jasonikakis Jan 6 at 13:29
• The datasheet is on the website you included in your question! Scroll down to where it says "CHQ1838 Datasheet". Use Google to search for the definition of a Pullup Resistor. And as to 91K: is it more than 20K? Yes. Will it do? Don't know until you try it. – CharlieHanson Jan 6 at 13:36
• ok thank you so much! i will try it – Jasonikakis Jan 6 at 13:38

I can’t read the language of the datasheet but, from the schematic it contains, this chip detects a 38kHz IR carrier, and grounds its output when it detects one. Hence, the output is “normally high” (albeit somewhat-high-impedance), hence the “constant flow of current” you experience.

The schematic below should work for you:

simulate this circuit – Schematic created using CircuitLab

• Is that supposed to be the complete circuit? – Jasonikakis Jan 6 at 14:01
• Not exactly, you still need your battery, and your 7805 voltage generator. – user2233709 Jan 6 at 15:39

Logic output from the OUT pin idles at the supply voltage (+5V), and goes down to zero volts when the IR-receiver sees a burst of 38 kHz light. When it goes down, the transistor inside may provide enough current to light a LED directly. R1 might be made smaller, perhaps down to 100 ohms:

simulate this circuit – Schematic created using CircuitLab
The LED should only light when a TV-remote signal is received. Many TV-remotes keep sending repeated codes while a button is pressed: the LED will blink repeatedly.

• I don’t think it is sane to load the output that much. The datasheet says the pull-up resistor should be $> 20 \rm k \Omega$. – user2233709 Jan 6 at 15:38
• @user2233709 It may be OK if the LED is the only load. Should "OUT" be required to drive a logic device as well as the LED, your caution is well-advised. I have tried this circuit (with a different IR-receiver), and LED illumination was satisfactory. – glen_geek Jan 6 at 15:55