TSOP4838: received values differ in respect to power supply

Hi everybody,

I got the following issue:

I have 3 TSOP4838 IR Receivers working perfectly fine on my Arduino Nano. But if I use a different 5Vpower supply - for testing I used a Mega - they transmit wrong values. They still receive a signal when sent, but the values are off.

The Setup:

The 3 Receivers connected in parallel to power, ground (of the Mega) and the signal pin of the Nano.

What could be the issue with my setup and what could possibly help?
It would be great to find a working solution such that I only need one wire going to the Nano and supply the Receivers from a different source.

Thanks for looking into it!

Show us a good schematic of your circuit. Show us a good image of your wiring. What voltage are you measuring?

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In theory, if your sketch already worked well on Arduino Nano, it will be running normal on Mega. So for eliminating errors, you should use the same power supply and set frequency of Mega equal to the frequency of Nano. Good luck.

Thanks you two.

@KatyaS The Sketch works perfectly fine on both devices - the issue is all about where the TSOP Receiver gets its power from.

The Sketch is running on the Nano and the Receiver Pin is connected to the nano - only 5v power and ground are connected to the mega. Eventually i want to replace the mega with another 5v power source / a battery.

If i change 5v Power and Ground of the receiver to the nano, I receive coorect values. If I change them over to the mega, the Values received are wrong.

@ LarryD: I already found the software for the nice arduino scematics - I should find the time to do it over the next few days. Which Voltage should I be measuring? Of the Receivers Output/Signal? Power and Ground are the regulated 5V of the Mega and i put 100Ohm before the receiver.

So here are my scematics. I had to replace the nano with a micro and the mega with an Uno, but that shouldn’t make a difference.

Any guesses why Setup 2 will give me wrong IR results?

You may have a split power rail proto board, show us a picture of the actual wiring.

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It seems you haven't connected Nano ground to sensor ground when you power from the Mega. Leo..

The power rail is not split and the receiver is powererd. It only transmitts wrong results.

Wawa, that is right - is it necessary for the sensor and arduino to have common ground to decode the signal propperly? Would there be any way to avoid that / to power the Sensor separately from a battery with only one wire going to the nano?

Mojay: Wawa, that is right - is it necessary for the sensor and arduino to have common ground to decode the signal propperly? Would there be any way to avoid that / to power the Sensor separately from a battery with only one wire going to the nano?

Current needs two wires. Power uses + and ground of the sensor. Signal uses out and ground of the sensor.

Why one wire? Leo..

Of course it does, but is ne missing common current between the signal receiving arduino and the TSOP itself the source of the issue/ the wrong results? I might test that. But it still would not explain why it gets me wrong results then.

One wire because there willbe some distance between the arduino and the TSOP receiver and it would be easier to use just one wire instead of having to get 3 long wires from the arduino to the receiver.

Basically the question is which influence power&ground have on the signal integrity of the TSOP receiver... why do i get false results simply by changing the power source?! Voltage and current stay the same.

Mojay: . . . The Setup:

The 3 Receivers connected in parallel to power, ground (of the Mega) and the signal pin of the Nano. . . .

This is not clear from your schematic which shows only one receiving sensor (TSOP4838). Are you attempting to use the same signal pin for all three sensors, so the outputs of the three sensors are directly connected to each other ? You can connect multiple devices to the same arduino pin, but then you must use one diode per device to separate them (or some other form of "OR" gate) otherwise they fight against each other.

3-pin IR receivers have open collector outputs with weak pull up resistors. So it is possible connect a few in parallel without a diode OR. Leo..

Wawa:
3-pin IR receivers have open collector outputs with weak pull up resistors.
So it is possible connect a few in parallel without a diode OR.
Leo…

OK. I’ve just looked at the data sheet and this is indeed correct. I’ve learned something. I guess as long as the devices are well matched there should be no problem.
The datasheet , however, shows a 100 Ohm resistor in the +5 volt line where the OP appears to have a 1K resistor.

Fritzing....

A 100ohm resistor is mentioned in the text.

Leo..

Yepp, the resistor rings are not right, I couidn't get them to change. But its 100ohm.

Soooo, any other guesses what the issue could be?

Are you using one 100 Ohm resistor and one capacitor (say 0.1 uF) per TSOP device or are all 3 TSOP devices sharing the same decoupling circuit ? Your schematic does not show the situation you have described with multiple TSOPs.

There is no signal return path on the Nano in the second picture, put a jumper from Nano GND to Mega GND.