Short range, several channels, ping only radio comm - Page 1
Forum section: electronics / projects

author: tester43
author_rank: Regular Contributor
timestamp: January 25, 2023, 12:55:55 pm
content: Hi,I have an idea for a minimal size radio trigger. It's used in photography to put strobe light away from camera without cable.Camera is closing 2 pins when it wants the strobe to fire.Design idea is having N amount of triggers. When 1 of them gets the closed pins (interruption), all remaining in the group also do some action.I am considering what to use as a solution for radio.BT seems to have a high latency.WIFI sounds like extreme overkill.I would like to avoid analog solutions if possible (i.e. no protocol, just a frequency generated).I assume:- Low power consumption.- Up to 4 channel communication- Small physical size- Latency between 10-20ms should be acceptableWhat would you recommend reading about?

author: CountChocula
author_rank: Unknown
timestamp: January 25, 2023, 01:39:47 pm
content: Hi! You don't say whether you're looking for a completely self-contained solution or if you could (say) have some sort of intelligent control (like an Arduino) in the loop. If the latter, you could look into one of these433MHz bandcontrollers that are available. They're pretty inexpensive and work reasonably well (though be careful, there are some terrible-quality ones being sold on Amazon, so I'd stay away from those).If you're looking for something more self-contained, there are modules based on the same tech that behave like remote switches; I suspect it's possible to configure them so that they work so that a single transmitter can trigger multiple receivers. Just search for “433MHz remote switch” and I'm sure you'll eventually find something that works for your needs.In both cases, I think it will be hard to synchronize them (like you would to trigger multiple flashes to go off at the same time, for example), so it might not quite work out. If so, I would consider some line-of-sight alternative, like IR, whose response times I think can be a little more predictable.Either way, please let us know what you end up discovering… I'm looking into this same tech for a problem I'm trying to solve myself, so very interested in learning what has worked for others. Cheers!—CC

author: Siwastaja
author_rank: Super Contributor
timestamp: January 25, 2023, 01:51:02 pm
content: Depends on what you are comfortable with. If you are "at home" working with microcontrollers, specifically ARM Cortex-M devices with bare metal toolchain, you will have nRF52 or similar MCU running raw radio protocol of your choice in matter of hours (look at the datasheet of RADIO peripheral, it's quite simple). 10ms latency is easy. I would do it with nRF52, just configure with some simple packet structure like 1-byte address and BLE LR signalling. Send a message with short (or zero length) payload and trigger a photo-mosfet or similar when you receive ADDRESS interrupt. Quickly looking at my calculations, nRF52 in BLE LR physical mode transmits a full packet with 1-byte address and zero bytes of payload in 510 microseconds. And this is with the slowest mode (125kbps BLE LR). Heck, for your 10ms target, you can still successively send the packet at three different frequencies and make the receiver alternate between listening those channels and still hit the goal.If you need a fairly reliable trigger, then working on any license free frequency band is going to require some engineering, because instead of being guaranteed absence of interfering devices, you have the opposite guarantee: other incompatible communication and even non-communication devices will pollute your band.This is how I would do it. OTOH, if you are not familiar with microcontroller programming, then some prefabricated module would be the answer.

author: tester43
author_rank: Regular Contributor
timestamp: January 25, 2023, 02:00:44 pm
content: super kind, precise and usable answers - thank you everyone - when I have something, will report back

author: cantata.tech
author_rank: Regular Contributor
timestamp: January 25, 2023, 02:05:57 pm
content: IR (infared) on a Microcontroller, Arduino/ESP32/rpi is generally speaking pretty easy and interesting.Once you have a basic setting going, then you can extend it across microprocessor systems.In terms of data, it's easy to load different data into the IR packet by changing the code. For example, you can embed a 'color to flash' or 'time to flash' information in the IR Code itself.Whilst consumer electronic typically use one ir-hex-code for one function, there's no reason why you can't bit shift your data and have it do different things.

author: tester43
author_rank: Regular Contributor
timestamp: January 25, 2023, 06:46:11 pm
content: Hi,thank you, but I ruled out idea of IR for some reasons:1. you have to grant the visibility of emitter and sensor all the time.2. limited range3. limited use in daylight over bigger distances (i.e. 10-20 meters)I think I will go with nrf52 route