Momentary RF switch trigger time seems to vary. Any way to make it reliable and consistently fast?

Thread Starter

Taymar

Joined Jan 13, 2017
34
Hi all,

I have a couple of these pre-built RF switches. There's a fob with a single momentary button and an LED. The receiver has inputs and outputs for power.
https://www.amazon.com/gp/product/B08F7T2THH/ref=ask_ql_qh_dp_hza

The default operation is that the receiver switches the output on while the transmitter button is held. You can short a couple of pins and change the mode to on/off vs. momentary.

The problem I am having is that I need it to respond very quickly, every time. right now the time to activate seems almost random. If I click the button repeatedly, the output will switch on maybe 1 in 10 times (and not with an equal amount of fails inbetween). If I slow way down and press/hold the button, it's better but still not perfect.

I wondered if maybe there's a capacitor or similar I could swap out or remove that might make the response time more consistent, or if I should look elsewhere for a similar product.

Thank you for any suggestions.

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Thread Starter

Taymar

Joined Jan 13, 2017
34
I have since found a datasheet on the main IC, a SYN500r:

http://www.xie-gang.com/SYN500R.pdf

It looks like there might be some good info in here, sadly it's a little out of reach for this electronics novice. I'm having a hard time following the IC's traces on the board to try and make sense of the circuit diagram. It does sound like by leaving pin 7 and pin9 open, it increases the baud rate. I snipped the legs but didn't notice any difference in operation.

I'm also wondering if it might be due to the device entering power off mode after each button press. PIN 8 supposedly handles that but disconnecting it from the PCB makes the whole thing stop working. I may need to also remove 'R3' per the datasheet, but have no way of knowing which component that is on my board.

Last guess is perhaps it's over-zealous noise filtering. it's definitely very strange that sometimes it triggers imperceptibly fast while others it takes almost a full second to register.

If there are other affordable and compact technologies I should look at instead of RF, I'd definitely appreciate any ideas please. thank you!
 

OldTech

Joined Jul 24, 2009
6
I have since found a datasheet on the main IC, a SYN500r:

http://www.xie-gang.com/SYN500R.pdf

It looks like there might be some good info in here, sadly it's a little out of reach for this electronics novice. I'm having a hard time following the IC's traces on the board to try and make sense of the circuit diagram. It does sound like by leaving pin 7 and pin9 open, it increases the baud rate. I snipped the legs but didn't notice any difference in operation.

I'm also wondering if it might be due to the device entering power off mode after each button press. PIN 8 supposedly handles that but disconnecting it from the PCB makes the whole thing stop working. I may need to also remove 'R3' per the datasheet, but have no way of knowing which component that is on my board.

Last guess is perhaps it's over-zealous noise filtering. it's definitely very strange that sometimes it triggers imperceptibly fast while others it takes almost a full second to register.

If there are other affordable and compact technologies I should look at instead of RF, I'd definitely appreciate any ideas please. thank you!
The problem you are experiencing is typical of these cheap remote control modules. It's a multi-faceted issue. First problem is the data rate being used, and it's limited by the particular chip being used in the system. The second, and probably the most significant, is the length of the data stream being sent by the transmitter. I didn't investigate the specifics of that issue in the datasheet of the chip, and you'll need a scope to see it if it's available on one of the chip's pins. It's probably a fairly long stream of 1s & 0s, and likely to be unchangeable by the designer or user.
Another issue to be contended with is the AGC response time in the receiver. It can vary, depending on the strength of the transmitted signal, and ambient RF noise in the passband of the receiver.

If a fast response time is critical to you, you'll probably need to find a better (more expensive) remote control unit.
DaveM
 

Ya’akov

Joined Jan 27, 2019
6,853
If you need low latency and guaranteed response a cheap 433MHz ASK remote set isn't going to cut it. the BER (Bit Error Rate) is probably very high because of poorly matched antennas and tiny RF power outputs.

You might be able to improve things if you put a better antenna on the receiving side (since the fob isn't suited to that), or you can buy one of the "long range" sets that have telescoping antennas on the remotes. If you really need snappy response, you might have to make your own fob with something like a 915MHz module with a better modulation scheme like GFSK (Gaussian Frequency Shift Keying).

The ASK (Amplitude Shift Keying) choice is cheap and sometimes cheerful but often just doesn't cut it.
 

RPLaJeunesse

Joined Jul 29, 2018
222
The data sheet calls for a 167mm/6.6" antenna. Are you using one (attached to the single small corner via hole)? It needs to be a straight wire and away from any metal.
 

Thread Starter

Taymar

Joined Jan 13, 2017
34
Yep I am using the stock antenna it came with - tightly coiled. I will give that a try too out of curiosity, thanks!

I'm not sure if I will stick with the new remote I got (it's still very cheap), if I were looking for something more sophisticated, might you have any suggestions on where or what I should look out for?

Thank you so much guys for the help.
 

Ya’akov

Joined Jan 27, 2019
6,853
The data sheet calls for a 167mm/6.6" antenna. Are you using one (attached to the single small corner via hole)? It needs to be a straight wire and away from any metal.
These modules usually use coiled antennas to save space and the cheaper ones just use a piece of solid core wire which is never going to maintain its shape, and the slightly better ones use a much stiffer plated steel one. In either case there's no ground plane to speak of and the match is going to be very iffy.

I know from playing around with these modules that the match is very touchy and the output of the transmitter is highly affected by a poor match. Just cutting a piece of wire to the specified length isn't going to ensure a good match. A 1/4λ on 433.92MHz is 172.84mm, so I don't know why it is specifying ~5mm less which isn't a trivial amount.

I do think that a better antenna could make a difference, and since it is nearly free to try, it would be worth doing. Including a 1/4λ ground would also probably help.
 

Ya’akov

Joined Jan 27, 2019
6,853
Yep I am using the stock antenna it came with - tightly coiled. I will give that a try too out of curiosity, thanks!

I'm not sure if I will stick with the new remote I got (it's still very cheap), if I were looking for something more sophisticated, might you have any suggestions on where or what I should look out for?

Thank you so much guys for the help.
How much are you willing to build yourself?
 
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