Category Archives: microwave

Microwave for the Weekend

tmp2DA0If you read the blog about the Maker Faire, I just came back with a bag of goodies and one of them is a microwave movement sensor.

Not the two-board solution I discussed a while ago that never really worked – this is a small, neat single board called an RCWL-0516 and here’s a Chinese link though if you get in touch with the fellow I mentioned at the Faire where I got mine – ABX-LABS (Ebay shop) he might have them. About £1 anyway.

So this board has 5 wires and not a lot of information out there, some of which is in Russian. I did found out enough to know that this unit is oscillating at around 3 Gig and you only need to use 3 of the 5 wires!

The unit will pick up movement up to 7m away and in the right circumstances can see right through wood! No silly comments about being irradiated please.

So I set it up on my bench, the 3 wires of interest are ground (obviously) VIN and VOUT. Stick 5v on VIN (will not work on 3v3) and a LED on VOUT – and you’re done – it works.

Well, that was easy and of course it WAS too easy. I took the board and applied it to one of our ESP8266 boards which have 5v – and took the output to Pin 14 which in the case of my software, is a de-bounced input which can send an automatic MQTT message on change.  Job done – except – it would not work. It seemed over-sensitive but after more careful checking – it really wasn’t taking too much notice of movement – instead triggering fairly regularly ALL ON IT’s OWN!  I tried putting a cap across the power, I tried putting a cap across the output – all to no avail.

In the process of having a gripe with Aidan that we’d been ripped, I put the board on my standalone test to show him it working – and decided to route ground and signal back to the ESP – it worked perfectly – then it twigged -  ESP8266 boards are prone to putting spikes on the power lines when transmitting!  I put a 10r resistor in series with the power and a tiny 330u 6v cap to ground at the Microwave board end – problem solved.

If you want to do something clever, the 16 pin logic chip – I stuck a scope on it and pin 12 gives off some interesting analog stuff!

In terms of sensitivity it pretty much works 360 degrees though supposedly it is most sensitive on the component side of the board direct on.

I spend half of my time waving my arms about at the normal room IR sensor to keep lights running – this I think will be MUCH better.

Have fun.

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Microwave Radar

tmpBA87As soon as one mentions “microwave radar” I’ll bet you’re thinking “expensive” – well how does under 2 quid sound…

http://goo.gl/BgwcbZ

These little devils are movement detectors, bought from Ali Express on a whim and they use the PCB as the antenna (3Ghz) – hence the ridiculously low price. So just a quick one – I ordered 2 and they arrived the other day – I’ve hooked them up to 5v (they work from 3v3 to 20vDC) and use less than 3ma. 3 pin connector gives a positive output on movement – and the output stays high for around 30 seconds.

Updated April 2017 - see also http://tech.scargill.net/microwave-for-the-weekend/

On the back there is a pair of connection points (soldering iron needed) and if you put a 10k resistor across them (I found this out by trial and error as there is very little info on these units – at least in English) the pulse goes down to around a second. VERY sensitive and although I’ve only done the briefest of tests I can confirm they can detect hand movement through 0.5” of chipboard !!

According to the blurb they pick up movement 360 degrees and have a detection of 6-9 metres. Applications include security, intelligent lighting, toys etc.

What I DID find when testing this and a later model (see above) is sensitivity to power supply - it is probably no good sticking it on the same supply as an ESP8266, the noise spikes will make the board unreliable. My solution is a 10r resistor in series with the 5v supply - and a 330u 6v cap (from the microwave board end of that resistor) - to ground - works a TREAT.

Both sensors work well, let's have your thoughts  (no theories about getting cancer from radiation please).

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