Help with powering the Simple T4 RF receiver

Ok, so I’m very new to electronics, but I’m using a T4 RF receiver in my project and I’m powering it with an Adafruit 3.7V 4400mAh battery. I’m an idiot and only after soldering my entire project together did I realise it says +5V. Does it need 5v or more to work or am I good with 3.7V? If it does need more, is there way to boost it?

Might work. Won’t hurt. Won’t work the best. Sensitivity may be lower than specified.

Datasheet says operating voltage from 4 to 15 volts for the chip on the board. The rest of the board seems specified for 5V. Check the voltage of your battery, it can be a range of values depending on the state of charge.

I’d say as the voltage falls too far, the oscillator may not start, and so it won’t receive data. Exactly what voltage does this will depend on manufacturing variances. You could test it.

Thanks. Checked with my multimeter and it’s actually hitting about 4.05 on average. Seems to be working ok right now. Will need to test sensitivity probably, but in most cases it won’t get further than a few meters. Being RF means it can penetrate through materials to an extent yeah?

Be with you in a little bit.

Thank you! Just tested the range really quick and it’s pretty abysmal, like 30cm or not even… So I guess I’ll need to boost the voltage. Is there something I can add that will do that? No rush, and thanks for dealing with my annoying newbie questions haha

Sorry, got an interrupt here.

30cm is a bit low; but it depends on the transmitter; show us your transmitter assembly?

Yes, RF can penetrate a bit, but keep both antennas at least 95cm from any metal to increase the range. This is usually quite hard to do, so don’t stress over it.

Also, just checking, if you’re in Australia you are limited to ten microwatts under the Radiocommunications (Low Interference Potential Devices) Class License, and that won’t go far. I’d normally choose a 433 MHz pair of devices in Australia.

Also, I’ve had these sort of range tests fail because someone nearby had a doorbell or weather station transmitting noisily. Have you any way to check for interference on the frequency when you aren’t transmitting?

I’m curious. Can you tell me what voltage the Arduino Pro Mini board is being run at? It looks to be either a 3.3V or 5V variant, and I can’t tell which from the front face. It would have to be a 5V variant in order to run the receiver at 5V as well, otherwise the data lines would need some sort of level shifting (i.e. resistor).

I’m going to predict the sensitivity and therefore the range might not be terribly affected by the voltage you operate the receiver from. If it were on my bench, I’d try different voltages to see. The long wires powering the receiver could be a problem, and I’d check for that by watching the voltage with an oscilloscope. Might need a local capacitor near the receiver.

What’s the circuit on the bottom right? I’ve built several Arduino Pro Mini transmitter and receiver projects, but almost always powered the RF modules from the Arduino module itself.

No way to check that unfortunately. It’s the 415MHz receiver that Adafruit, and by extention Little Bird sells, plus the accompanying keyfob remote. Let me move it away from my computer and give it a test. It’s a part of what will hopefully be an RF controlled smoke machine, but for this test I didn’t have the smoke part connected. It is the receiver and an Arduino Pro Mini in parallel, plus a resistor and MOSFET I need to control the smoke machine. Which has some metal in it. And I assume the battery does too… The little coil on the receiver is the antenna right? I’m planning to have that positioned as close to the outer wall of the case as I can, away from the other stuff. Photo attached.

Testing somewhere that’s a bit further from my computer and stuff yields me even less. I’m beginning to suspect it’s the batteries in the transmitter, I might see if I can find some replacements and give that a go. Strike out all the variables you know?

It’s a 3.3V board, powered through the RAW connection point. Bottom right is the power cable for the arduino, plus a receiver and MOSFET that will hopefully be what lets me power the smoke machine portion. There’s a better photo in my other reply. Plus a switch that controls current from the battery. What would the long wires affect? I checked the voltage right at the receiver with a multimeter and it was still ~4V…

Yes, the twin CR18650 battery pack has metal under the blue.

Yes, the large black single-ended spiral on the receiver is the antenna. It should be left as it is, ideally.

Yes, batteries in transmitter can affect range. But they are usually lithium primary batteries with a ten year shelf life, so it is unlikely to be the cause.

Here’s how the long wires affect the receiver; the receiver draws current from the battery through the wire, so while the receiver is operating, and especially when it is decoding a transmission, the current varies at very high speed. The length of the wire increases effective resistance, and so the voltage experienced by the receiver may not be stable enough. A multimeter isn’t fast enough to measure that, you’d need an oscilloscope or data acquisition device.

If this is happening, then it is usually fixed by placing a capacitor between 0.1µF and 10µF at the receiver end of the long wires, in parallel with the wires. It acts like a storage, reducing the movement of the voltage during that critical time.

Ah thank you so much. In parallel… Ok I think I might be able to manage that. You think that will work, I don’t need to boost the voltage?

What uF do you think would be best? Or you don’t know without more info? I have to say, thanks hugely. I was so so stressed, you’ve been amazingly helpful and knowledgeable.

I’m not usually this responsive. You just happen to have piqued my interest, that’s all. :grin:

As the receiver is specified to work from 4V onwards, the operating voltage seems fine, so either it is faulty, the transmitter is faulty, there is ambient noise, or there is noise on the power input to the receiver.

The only way to know right capacitance is to measure the problem, and I take it you only have a multimeter. You might try the AC voltage setting, to see if it measures any tiny change during the transmission, but it is unlikely. Most meters don’t do that well. If it does measure something other than 0.00V AC, then how much it measures may be an indicator of the noise on the voltage induced by the receiver. However, the easy way out is to guess and multiply the capacitance by ten. I’d hesitate to use anything above about 470 µF because turning on the receiver may take too long. The datasheet says nothing about how quickly the power should turn on.

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I’ve developed two alternate theories.

encoder address does not match decoder

Check that the trinary address configured in the transmitter fob matches the address configured on the back of the receiver module. If there is any difference, even a solder bridge, then the receiver should be ignoring the transmissions except when they happen to be nearly right, which could happen when the transmitter is too close and causing noise.

receiver operating from different voltage to arduino

The Arduino Pro Mini takes the 4.05V and regulates it to 3.3V for use by the atmega328. The receiver takes the 4.05V to operate the radio, and the decoder chip, and the digital output pins are slewed between 0V and 4.05V when a valid transmission is received.

When an output pin is slewed to 4.05V, it will be 0.75V above the maximum voltage for use as input to the atmega328. Consequently the atmega328 input pins will shunt some of this to the output of the 3.3V regulator, and depending on the drive strength (unspecified in the PT2272 datasheet) may cause damage to either device, or just misbehaviour. It might, for instance, cause the PT2272 to stop decoding instantly. I don’t know what your code does, so I don’t know how likely it is for it to miss a short pulse.

Adding a series resistor of 220Ω to 1kΩ to the four digital output pins would fix this.

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Thanks. The receiver is marked in the description as no addressing needed, so I hope it’s not that haha. I am gonna order a 10µF capacitor like you said, and a few extra resistors and see what works. Neither should be too hard to add, so I’ll play around and see if I can get it to work. You were right about the multimeter, mine just showed 00.0 the whole time for AC… oh well. I seriously don’t know how to thank you enough for all this!

Good morning. Yes, you can hope, but you can also test. Long post.

When I buy half a million modules, I’d ask the factory to show me their test process. The steps they go through after making them to make sure they work. They might have no such process, instead relying on people to figure it out themselves. They might have an extensive process, with robotic probes that reach out and touch the module.

The receiver module has on the back a row of closely spaced address pads, with +5V and GND traces next to each. Their intention is that if you want to use a different address, so that you can use more than one of their product, that you will add solder to bridge some of the gaps. So they made the gaps really small, and they printed the solder mask in a way to leave an area of copper that was tinned in readiness and to prevent oxidation.

During that tinning process, which is done also for other parts on the board, there’s a chance that the solder will bridge one of the address pins to one of the power supply traces.

If they don’t test for that, then you ought to.

Given the price of the product, and the lack of space to apply a test probe, and the lack of other markings, I think it is unlikely that they tested for it, and instead relied on either visual inspection of a batch, or a statistical visual inspection of a percentage of units. The hope and pray method.

So there’s a few ways to test;

  • set up a microscope or other magnifier and check the address pins very carefully under different angles and light colours, on both the transmitter and receiver,

  • set multimeter for DC volts to cover a range of up to 4V, attach the multimeter black lead to the GND pin or negative of the battery, turn on the receiver, and with the multimeter red lead probe each of the address pins on the receiver, writing down the voltages on each. Each should have a nominal voltage that is not zero and not 4V. If any of the pins have zero volts or 4V, then there’s a higher chance of invisible solder bridge.

  • do the same two steps for the transmitter.

An invisible solder bridge can be removed by scraping, or sometimes heating with a soldering iron, but you have to be careful not to add a solder bridge that way.

This problem has happened before for me, back in the 1990s, using MC145026 chips, which are similar in intent to the PT2272. In one situation, I solved it by setting each address pin to GND, on transmitter and receiver, and everything started working. My best guess is that there was a solder bridge that I missed.

These days, I’d use my digital storage oscilloscope (DSO) or another acquisition device to check the radio transmission data. A DSO can be attached to the battery of the transmitter fob and check the data by capturing the changes to the battery voltage. Or a DSO can be attached to a small signal diode hanging in the air next to the transmitter. Or a software defined radio can be used to receive and display the signal.

Oh, and make sure you are not touching the address pins when you test. Touching them is enough for the PT2272 to believe a different address is needed.