Pre-certified module for short-range transmission of 1-bit signal - Page 1
Forum section: electronics / rf-microwave

author: pylo
author_rank: Regular Contributor
timestamp: January 06, 2019, 01:51:59 pm
content: Hi!I'm in need of something for my next project and I'm looking for some help, given that I lack the needed experience.What I'd like to do is transmit an ON/OFF signal (just a single bit of data) to 1-2m distance at most, in a single direction (only one party sending). There is no need for any security whatsoever, this is a completely non-critical application security-wise.While it might be relatively easy to hack together something like this at home, I need this for a future product. As this would constitute an "intentional radio emitter", certifications down the road (FCC, RED, etc.) would be much too cost-prohibitive and unfeasible (I guess/think?) for a home-brew solution. I was hoping somebody here knows apre-certifiedmodule, such as those available for BT or WiFi where certifications later on are greatly simplified, only, you know, simpler. Something like a dumbed-down wireless garage opener (with shorter distance and no security).One option is of course to take a pre-certified module for a more complicated "technology", such as a bluetooth, and use that, but that is totally over-engineered for my needs. Well, it could be plan B (if everything else fails) actually, but I was hoping there is a module that is closer to my "barbaric application", as that is potentially both cheaper and smaller (I need size to be small).Or maybe somebody knows a 3rd solution that could fit me?Thanks for your help.

author: sokoloff
author_rank: Super Contributor
timestamp: January 06, 2019, 01:55:34 pm
content: I'd start by looking at the 433MHz band transmitters; should work fine here, depending on the data rate. (I'm assuming from the question that the data rate is quite low, on the scale of human button pushes, but you didn't state explicitly.)

author: pylo
author_rank: Regular Contributor
timestamp: January 06, 2019, 02:00:28 pm
content: Quote from: sokoloff on January 06, 2019, 01:55:34 pmExactly, it is actually for button pushes. Meaning I have no requirements for data rate (ok, let's make it 5bits/sec), but the action should be conceived as "instantaneous", so I do have a latency requirement (something around or below 50ms is ideal, but I guess that's not a problem).

author: wraper
author_rank: Unknown
timestamp: January 06, 2019, 02:08:18 pm
content: Quote from: pylo on January 06, 2019, 01:51:59 pmSounds like it doesn't need to use radio to begin with. Usually IR is used for something like this.

author: pylo
author_rank: Regular Contributor
timestamp: January 06, 2019, 02:10:47 pm
content: Quote from: wraper on January 06, 2019, 02:08:18 pmIt needs radio, because there will be no direct line-of-sight between transmitter and receiver.

author: Nusa
author_rank: Super Contributor
timestamp: January 06, 2019, 03:13:26 pm
content: How about audio? Whether it's within the human range of hearing is up to you.A cellphone app could do that if you pick the right frequency and you wouldn't need to build a transmitter.A dog whistle would be another version of an audio transmitter...extremely cheap, too.Of course a cellphone app could also do bluetooth or wifi, so there's a prebuilt certified radio solution there as well.

author: pylo
author_rank: Regular Contributor
timestamp: January 06, 2019, 04:17:21 pm
content: Quote from: sokoloff on January 06, 2019, 01:55:34 pmI'm still looking into these, but a search on Google and DigiKey mostly turned up modules that were either considerably larger or more expensive than some BT modules I've used in the past. One that could be promising though is Quasar's QAM-TX3, but from the looks of it it only got CE approval. I'll be contacting them tomorrow though for more information.Quote from: Nusa on January 06, 2019, 03:13:26 pmNice thinking out of the box! My application does not lend itself to smartphone-use, but still, using a piezo tweeter and a suitable mic (any one from here for example) might just do the trick. And the product wouldn't even qualify as an intentional radiatorI do can think of a few possible troubles, like the processing power needed at the receiver (it is battery-operated) or how it affects pets. Nevertheless, I think this is worth inspecting.

author: mark03
author_rank: Frequent Contributor
timestamp: January 07, 2019, 04:19:39 pm
content: Re: audio, you could in theory do the transmit side without electronics. That's how the original television remote controls worked. They were acoustic (ultrasonic) devices where a button press would strike a tuning fork. Batteries not required!

author: ThomasDK
author_rank: Regular Contributor
timestamp: January 07, 2019, 05:59:40 pm
content: Quote from: pylo on January 06, 2019, 04:17:21 pm433 MHz is an EU only band, you need different frequencies for other parts of the world. If you want a single world wide frequency, go for the 2.4GHz band. Zigbee or BLE is probably the cheapest options these days for something pre certified.Another option could be MRF89XAM8A (EU) and MRF89XAM9A (US/Canada).

author: Nusa
author_rank: Super Contributor
timestamp: January 07, 2019, 06:28:05 pm
content: Quote from: mark03 on January 07, 2019, 04:19:39 pmI remember those. But children, which I still was at the time, were the original remote controls. For some stations (there weren't that many), we needed to adjust the rabbit ear antennas after changing the channel.

author: soldar
author_rank: Super Contributor
timestamp: January 13, 2019, 01:11:33 pm
content: Quote from: pylo on January 06, 2019, 01:51:59 pmSounds like a remote garage door opener or ceiling fan control would work. You can get those for close to nothing.

author: macboy
author_rank: Super Contributor
timestamp: January 18, 2019, 07:41:01 pm
content: Look up "24YK-RX" and "24YK-TX". They are around $1 each module. These are a transmit and receive pair of modules which do all the work for you. It doesn't get simpler, and you couldn't build it cheaper.For the Tx, you supply power (3 V coin cell works great) and 1 to 6 buttons. Quiescent current is so low you simply keep the Tx powered all the time. The Rx module has six outputs corresponding to the buttons. It can be set up to toggle or normal mode. In normal mode, each output is on (active high) when the corresponding button is pressed. In toggle mode, each button press toggles the output. Each Rx can be paired to more than one Tx; the Tx sends the identity of the Rx so that other Rx modules will ignore the signal. That does not make it secure, but it makes them able to coexist with other modules without interference. The Tx and Rx modules are superficially identical and are actually transceivers, not simply transmit/receivers.

author: splin
author_rank: Frequent Contributor
timestamp: January 28, 2019, 11:54:23 pm
content: Quote from: macboy on January 18, 2019, 07:41:01 pmHow does this address the OP's primary requirement?QuoteTo what extent does pre-certification reduce the cost of certification of the complete poduct given that emissions can be affected by factors external to the module such as the power supply, wiring and especially software in the case of more sophisticated modules? It should greatly improve the chances of passing the tests first time but is a simplified test procedure allowed when using pre-certified modules?Does the same apply in Europe? I'm guessing you are not allowed to self-certify as you are for the CE mark?

author: Lord of nothing
author_rank: Super Contributor
timestamp: January 29, 2019, 10:18:13 pm
content: QuoteWrong!

author: TheSteve
author_rank: Unknown
timestamp: January 29, 2019, 10:22:37 pm
content: Digi xbee's are gold, but likely way out of your budget.

author: jmelson
author_rank: Super Contributor
timestamp: January 30, 2019, 11:26:27 pm
content: On eBay, you can find "4 channel remote" devices. They have a little key-fob transmitter with 4 buttons and a little PC board with 4 outputs. We cut these apart and put them into our own control modules. They were about $4 each from China. Here's the exact one we used :https://www.ebay.com/itm/4-Channel-315MHz-Remote-Control-Receiver-module-Decoder-SC2272-M4/301694945179?hash=item463e6b879b:g:CwMAAOSwd0BVsKau:sc:USPSFirstClass!63130!US!-1:rk:6:pf:0Now, these turn on one output while the button is pressed, so you'd need to add some kind of on/off latch to get your <whatever> to toggle on/off as desired.Jon

author: splin
author_rank: Frequent Contributor
timestamp: January 31, 2019, 08:07:39 pm
content: Quote from: jmelson on January 30, 2019, 11:26:27 pmAre these pre-certified as required by the OP?