Several NETMF-based commercial products have been popping up recently, so I thought I’d share my latest one. This serial multiplexer is in the final stages of testing. The only thing left to do is add the in-field update code.
This serial switch/multiplexer allows up to 4 RS-232 devices to talk to 4 other serial devices across a single serial channel, most commonly a radio. Let’s say you have 4 instruments (GPS, temperature sensor, compass, sonar, etc) each outputing serial data at their own baud rates, and you needed to transmit that data across 10 kilometers. If you don’t want to buy 4 separate radios for each instrument, you could use this multiplexer, which will combine the data from each source and seamlessly serialize them into a single stream fit for transmission through a single RF channel. At the other end, another one of these boards will decode the stream and split them back into 4 separate serial streams. The process is transparent to all devices, and as far as they are concerned, the multiplexer board doesn’t exist at all. Data can be transmitted bidirectionally.
With managed code, the multiplexer can achieve 115.2kbps of throughput, which was our design goal. Informal testing has shown that it can probably go up to 152kbps, if RF channel capacity wasn’t a limiting factor. If RLP was used, it can likely achieve an even higher throughput.
It will be used in environmental monitoring, so power flexibility was an important parameter. Using an external battery, it can be powered anywhere from 7.6V up to 36VDC. It can also be powered entirely through USB if a technician in the field wants to use one of these with their laptop. An on-board power switch seamlessly transitions between both power sources and prevents one power source from flowing into the other power source if both are connected at the same time.
For size comparison, I’ve taken a picture of the old and new boards. The new board is quite a bit smaller and packs even more features than the old one. I’ve also shown the multiplexer mated with a high-power radio, which will be its first application, and there are several more products in our company that this board is destined to be integrated with.
I’ll try to post a video once testing is finished. Reams of invisible data streaming through the air probably won’t be exciting to watch, but at least you’ll get to see the LEDs blink 