I need to send a trigger to a sensor which is about 15-18 feet away from the micro. Of course one way is to boost the signal from the micro (on the trigger wire) using a MOSFET. This solution works but incurs some pains in routing that wire around my system.
If Bluetooth or Mesh is used instead (say by communication between an Argon/Boron to a Xenon connected to the sensor), what would be the lost time due to the wireless transfer? Are we talking < 2 ms or more?
I would appreciate the community’s input.
If you are planning on using mesh devices, mesh should be the primary choice.
As long both devices are active/awake at the given time, then the latency will be mainly impacted by your code reacting to the event on either side and the chosen transfer will be secondary.
Thank you @ScruffR but because it involves camera triggering on the connected mesh device, it is important to know approximately what that latency would be…?
I don’t think there’s a lot of empirical data on mesh latency yet.
I am just looking for an “order of magnitude” number for Bluetooth and/or mesh latency.
Given that these technologies have been around for a while, how long on average does it take the two devices to broadcast and receive a message? What are we talking about approx …
In Bluetooth audio, latency can be as high as 150 ms but this is primarily due to audio compression prior to sending rather than Bluetooth itself.
@Jimmie There is a lot to be said for using wired rather than wireless communication. If this signal is just a TTL pulse. You are also no doubt aware that a wire can act as an antenna and pick up stray electrical fields thereby inducing a potentially high voltage in the line. Opto-isolators and diodes plus current limiting resistors can be used or you run something like RS485 which is pretty tolerant to interference - this then makes the camera end more complicated as you would need an RS485 to TTL driver IC and a small uC ATTiny45 say to turn the serial signal into a camera switch signal. The upside is very low latency.
Thank you @armor. You raise good concerns that need to be taken care of.
I was trying to circumvent all of these issues by using a wireless signal (Bluetooth or Mesh) but before trying, I wanted to get some input on latency. If these technologies lead to latencies over 20-30 ms, I will have to stick with a wired connection.
Curious question and that had me wondering what the max data rate of the Layer 1 hardware is. The 802.15.4 standard has a max data rate of 250kbits/sec at 10 meters. To get more range and power savings I assume the mesh products will have a lower rate limit in the 50-100kbps. Doing the math on 100kbps, you can transmit 12.5 byes of data in 1ms. So you can make some kind of guesstimate such as perhpaps a local, single hop handshake takes 32 bytes. It would take something like 3ms to make that handshake.
If you transmit out to the cloud, you’re still looking at 20ms-2000ms+ response time depending on network conditions.
Thank you @ninjatill. This is good news as I am just sending a short pulse so 3 ms works