433Mhz RF Transmitter With Receiver Kit For Arduino ARM MCU Wireless

Hi all!

I ordered two pair. 433Mhz-RF-Transmitter-With-Receiver-Kit-For-Arduino-ARM-MCU-Wireless

The first pair of the receiver panel does not work, if it turned out 3.65v add DATA pin down firmly. Then the second pair ended in the inn, it is already working. Today again I started to deal with my project and I noticed that the receiver again wrong. I looked at 3.65v and also placed an order permanently. You ever experienced something like that? What can you do with it? Go to the trash?

Thanks! K.

Could you explain what you mean ? I don't understand. Can you tell which Arduino board you have, and how it is connected.

I use VirtualWire/RadioHead : http://www.airspayce.com/mikem/arduino/RadioHead/ And I changed the VirtualWire/RadioHead to enable the internal pullup resistor for the RX pin. That helps a little to get the voltage higher for my 5V Arduino.

Data pin fix 3.65v on receiver modul. Arduino leonardo and VirtualWire lib.

Communication:

Arduino pro mini +Trasmitter Arduino Leonardo +Receiver

I ordered two pair 433Mhz RF Transmitter With Receiver Kit. First Receiver dont working, because data pin fix 3.65v. I dont know why. Second Receiver working well (data pin 0-1V), but, two days later I experienced the same, data pin 3.65v and dont working.

Now you understand? Sorry for my bad english.

Yes, I understand :slight_smile: The data output of the receiver module is not changing, it is 3.65V.
I don’t know why it is doing that, I have a number of those and they all work.

The receiver module uses a LM358 for the data output signal. It it used in a auto-gain circuit. If the output is fixed at 3.65V, then something is wrong.

Do you have a lot of static electricity ? Or did you use 12V for the receiver module ?

Did you order from the same seller ? Perhaps it is a batch from the factory that is faulty.

MX-FS-03V.gif

I found this: wiki/433Mhz_RF_link_kit Receiver Data Output: High - 1/2 Vcc, Low - 0.7v

I do not think that would be the cause static electricity. I have used just about Arduino (output 4.86v)

I bought both packages at the same time a salesperson probably defective the factory. Nowhere else will you see such an error.

Where have you purchased?

Thanks. K

On Ebay. But I don't use the cheapest receivers anymore, because of the coil that is used to tune the frequency. I replaced them with receivers that use crystal for the frequency.

I dont know, could you link it to one?

For example this one : www.ebay.com/itm/361458616766 Or this one : www.ebay.com/itm/301694836703 I use this one myself : www.ebay.com/itm/181633631837 I also have a RXB12, but I forgot if it was better or not : www.ebay.com/itm/321765477124 This one is called a RXB6 : www.ebay.com/itm/200840057225

I got mine few days ago and they are the cheap ones from eBay (item #171063064043) and so far they have worked well without any issues.

I have not enabled the pull-up for RX pin because the input line rises to ~3.74V relatively fast when the receiver is receiving data and the signal looks good, see attached Signals.png picture. I tested by enabling the pull-up and the signal rise time did not change at all but instead the signal did not go to zero level anymore, thus I don’t think it is a good idea to enable it (and I’m not going to enable pull-up for my SW project).

I’m using RadioHead ASK driver for communication between two Arduino Uno boards.

BTW my receiver is getting “constant” data over the air (see Receiver.png) even though I’m not sending anything. Might be that there are other transmitters sending something with the same frequency but with the RadioHead ASK driver my SW is not getting that data.

TomiP, thanks for the pictures. If the signal is very faint, does the receiver still produce such a good signal ?

Those receivers have an auto-gain. If the transmitter is not transmitting, then the gain in the receiver is increased until noise is received. The RadioHead RF_ASK interrupt is thus triggered many times a second (up to a few thousand times per second is normal). What the RadioHead library does, is trying to make sense out of the noise ;)

What did you measure the voltage on the receivers data pin with? If you used a multimeter, that wont give a correct answer, as those types of receivers have a continuous stream of rubbish data on the data pin, which a multimeter will average and give a constant reading. You need to use a CRO to get an accurate answer.

Receiver Data Output: High - 1/2 Vcc, Low - 0.7v so not more than 2v. I measure the voltage 3.65v fix, not changed. I think the panel is simply wrong. I ordered new.

Koepel:
If the signal is very faint, does the receiver still produce such a good signal ?

Yes it seems that the signal is very good even though I removed the external antenna from the transmitter (and receiver to see how it behaves). But at the moment the receiver and transmitter are very close to each other and I cannot move those further away of each other so that might be the reason that the signal looks good even though there is no antenna.

Koepel:
Those receivers have an auto-gain. If the transmitter is not transmitting, then the gain in the receiver is increased until noise is received

Thanks for this piece of information, now I think that I understand what is happening in the beginning of the receiving. When the transmitter is not sending anything the gain of the receiver is high thus it is receiving noise, but once the sender starts to send data the receiver decreases gain automatically because it can receive the data with lower gain and that is the reason that in the beginning the receiver is receiving also other data than the 1kHz preamble (?) that the sender is sending. This is visible in the attached Preamble.png i.e. that receiver is receiving first plain noise (with high gain), then some noise spikes in addition to the actual signal (lower gain) and eventually the receiver is receiving only the data that the transmitter is sending (minimum gain).

Koepel:
What the RadioHead library does, is trying to make sense out of the noise :wink:

It is doing it very well, at least I am able to send “Hello, world!” between two Arduinos without any issues :slight_smile:

Kugynok, I'm not sure what is broken. The LM358 high output might be 3.65V, instead of 1/2 Vcc. But it is good anyway to compare it with another receiver from another seller.

TomiP, yes, the first pulse already changes the automatic gain, so that the signal from the transmitter results into a good output, and the noise is pushed down due to less gain. If you want to know what is in the air, try SDR. You need a receiver of 10 to 20 dollars and free software. http://www.rtl-sdr.com/rtl-sdr-quick-start-guide/ The 433MHz modules receive a wide band of frequencies, so it is hard to tell which is what. The SDR shows the different frequencies, that makes it very easy to spot the different transmitters in the neighbourhood.