Core Electronics Forum

Pololu RC Switch Question

Hi I have 3 Pololu RC Switch with Relays for channels in my 24V RC. Through the motor controller converts voltage to 5V to the receiver. I then made 2 rows of 6 LEDs (12 in total) all running in parallel with a resister to make each one 5V compatible. The LED circuit was tested on a 5V battery pack and works fine with all 12 LEDs coming on. How ever when I wire the receiver to the RC switch and then the LEDs, the LEDs do not come on. I have double checked the RC wiring connection via voltage meter and is ok. The negative is connected to the COM and positive to the NC on the switch. You can hear the RC switch trigger, and the flashing amber light on the switch goes from a slow flash to almost a constant amber flash. I tested the voltage and continuity from the receiver lead and then the external battery and both were showing 5V. I tested the same circuit on another spare RC Switch and again the switch triggered but the LEDs did not come on.

On a separate channel I am running an Adafruit soundboard with the RC Switch and it works fine with no issue.

I am new to this and any help as to why the LEDs are not coming on would be a great help.

Thanks Jade



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Hi Jade
You may have to post a circuit for what you have done. The photos don’t provide much of a clue.

Your text implies you have connected neg 5V to common and pos 5V to NC of the relay. In that case you have a short on the 5V supply and it has probably gone into some sort of protection mode and shut town. On relays NC means “Normally Closed”. It is unclear what you have actually done.
Cheers Bob

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Hi Robert93820

I have attached the diagrams of the circuits that I have tried. I have the AUX switch on the Transmitter in the off position when switching it on. At the RC Switch I have had it wired to the NClosed and then tried the NOpen position. same nil result with the LEDs not coming on.

Cheers Jade

0380_001.pdf (68.6 KB)

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Hi Jade
What is the part number of the RC switch. If it has relay output it will be isolated and you are not switching volts to the LEDs. you have simply connected the relay contacts to the LEDs and they are doing nothing. Post the type number so I can look at the circuit and advise.
Cheers Bob

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[quote=“Jade81311, post:3, topic:11779”]
I have attached the diagrams of the circuits that I have tried.[/quote]

The Pololu RC Switch with Relay has two parts - a RC switch and a relay. The switch turns the relay on, and you have confirmed this is working. For details on how to connect a relay to a load (the LEDs in your case) you can refer to the Core tutorial on relays:

The low power input circuit is the RC switch. The Control Circuit is the relay contacts and the LEDS. There is no connection between the Low Power Input Circuit and the Control Circuit, so the Control Circuit needs a power source for the LEDs, and that supply can be the same 5v that the switch uses. The Control Circuit power supply and the LEDs are connected so that the circuit is completed when the relay contacts are closed. For example, the wiring could run from the LED negative side to the supply negative (GND), the supply positive (+5v) to relay COM, and relay NO to the LED positive (resistor). That way when the NO connection is closed the circuit is completed and the LEDS will light.

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Hi Jade
Jeff has explained it all.
Connect the 3 wires from the receiver to the RC switch as you have shown in your bottom circuit.
The external LED supply is isolated from this. As Jeff said, connect the -ve of the ext supply to LED -ve, connect the +ve ext supply to Relay COM ( common), connect LED +ve to relay NO (normally open) and it all should work given you could hear the relay operating before.
Cheers Bob
Edit
By LED +ve i mean the positive side of the LED circuit including resistor.

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Thank you. They work perfectly now.

The next question if I were to add an Arduino UNO to add a flashing effect to the lights does the diagram in the pic work or would I have to power through the USB or Jack plug. I have made the coding block and it gives me desired lighting effect that I was after.

Thanks Jade

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That won’t work. The Arduino cannot power LEDs directly, and certainly not a whole set. You will need suitable relays between the Arduino pins and the LED sets. If you have an Arduino you can probably do away with the switch - code in the Arduino could recognise the RC signal and flash the lights. The diagram shows how it would be wired from the Arduino to the LEDs.

If there is a problem with getting the Arduino to recognise the RC signal then you can insert the switch as indicated - it is wired to any Arduino input that reads it as high (off) or low (on). The resistor to +5v would be about 10k.

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Hi Jade,

Welcome to the forum!!

The Pins of the Arduino are only able to deliver 20mA ( enough for one small LED with a current limiting resistor) but for larger arrays, you’ll need a relay which you already have. The Arduino is more for controlling specific parts of a project, lights, motors etc.

As Jeff mentioned you’ll need some interpreter to handle the reading of the RC signal and then make another output to open the relay module. If you haven’t already purchased a microcontroller yet I would go for a Raspberry Pi Pico, it allows you to send a very precise signal using the onboard state machines.

It looks like Jeff got his edit in before posting this reply, Jeff’s method would be much much simpler to implement it uses a couple more parts.

Liam.

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Thanks everyone for your help.

I put together Jeffs circuit diagram with some 5v relays and I was not able to get a response with any LEDs activating. Checked all connections and voltage. I then added in the RC switch and 10k resister, again same result with no LEDs activating.

As I am very green to the electronics I thought I would reverse engineer the above circuit and put together what I would work ie: all leds work off the 5V battery pack and supplying power to the circuit boards and switches ang go from there. Then slowly add in components.

I connected and soldered the LEDs in their groups and tested. I then supplied power, data and ground to the RC switch via CH4. I then connected the Arduino to CH5 Aux. Power was supplied to the Arduino. I then added in the power, relays and LED sets. Again I got no response from the LEDs, however the RC switch was tripping and the Arduino showed that power was on and data was being transferred.

I then simplified the circuit to see if the Arduino could directly power the LED sets as I know that a 5v external battery would. I plugged each set into the corresponding numbers 2, 7 and 8 (as per my coding) on the Arduino and saw them flash but not come on once I put a lead into the GND next to the 5v on the Arduino. The LEDs flashed on then stayed off. Realising that something set all the LED sets off, I noticed my mistake of putting the wire into the wrong GND, and moved it to the GND next to the PIN numbers. The LEDs then triggered in the pattern I had coded.

I then changed the NC to the NO on the switch so that the LEDs would trigger on when the switch on the transceiver is put in the on position. The circuit seems to be working fine with no issues at this stage.

Cheers Jade

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Those two GND pins are exactly the same - moving the connection from one to the other should make no difference. It is possible that when the LEDs flashed on but wouldn’t stay on the Arduino was tripping its internal fuse due to overload. If that’s happening that you could get inconsistent behaviour.

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If Jade is driving all those LEDs directly from the Arduino as it would seem from the description of actions taken the the Arduino certainly is overloaded. Wonder how long before smoke??
Cheers Bob

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If OP doesn’t have a few dead Arduinos at the bottom of the bits bin they they aren’t trying hard enough.

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Though that might be an issue that would come up based on your diagram. I will try to get one set of LED lights going with a relay. Then add the others in when its going.

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If you have got the lights flashing in response to the switch signal, then you are just about there - adding the relay into the circuit should be easy. Remember that the relay is just an electronic switch. If you look at the diagram carefully you will see how each relay is connecting its matching set of LEDs between +5v and Gnd.

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Given that I could overload the UNO running so may leads, I checked the current on each set of LEDs. The MM read 40mA per set for a total of 120mA. This seems low from what you guys are advising.

I check the current from the UNO pin with the red probe and the black probe to the light set +. Was this correct?

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Your description is " I then made 2 rows of 6 LEDs (12 in total) all running in parallel with a resister to make each one 5V compatible." I assume a ‘set’ is 6 LEDs, ‘each one’ means each set, ‘parallel’ refers to the LEDs, and the resistor is in series with the set. I can see that one set is yellow and one set is white, so the voltage drop will likely be 2.1v and 3.3v. If you run the LEDs at 10mA (which would be somewhat dim) then the resistors should be 330/180 ohm and the total current draw will be 60mA, That’s too high for an Arduino.

40mA as measured seems very small for that setup. Perhaps you have higher efficiency LEDs, or a larger resistor and much dimmer lighting. But even 40mA is right at the top end of what the Arduino can manage. You will get away with it for intermittent operation (flashing) but the life of the device will be shortened.

If you are using the setup in the diagram then the Arduino is the current source, and the +ve of the multimeter will go to the Arduino and _ve to supply the load, which could be the relay +, or the LED set +.

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From the datasheet for the ATmega328P (UNO micro).
Note: Absolute Maximum ratings, 40mA per pin, 200mA total.
This means you can draw 40mA from one pin; not all pins at the same time; and a total of 200mA.

Cheers
Jim

EDIT: I just thought of something else. Maybe the micro is setup so it will not deliver more than 40mA per pin regardless of the load on the pin. Therefore the actual current may be higher. Connect the LEDS sets to just a 5V supply and measure the current to see how much they draw.

Even though the absolute maximum is 40mA, you should not use more than 20mA. I tend to design to use 5mA maximum. The charts in the datasheet only go to 20mA anyway. If you need more drive, the mosfet, link below, has proven to work well for me.

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This is how you could wire the LED drive.
With 240 ohm resistors the current would be within spec of the 2N7000.
The current drain on the UNO Pin would be next to nothing as the Mosfet is a voltage device.
You could use 2 x Mosfets if you needed more brightness.
Cheers
Jim

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