Wired vs Bluetooth vs Mesh

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.

2 Likes

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.

2 Likes

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.

1 Like

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.

3 Likes

Thank you @ninjatill. This is good news as I am just sending a short pulse so 3 ms works :slight_smile: