Scargill

Archive for the ‘microcontrollers’ Category

Ok, so I’ve rekindled my interest in electronics with a vengeance. I’ve a load of gadgets I’ve been wanting and not finding anything reasonably priced out there I decided to get the soldering iron out and make them myself.

And so it was that I started looking at processor boards out there to make use of the popular Arduino design. I say design, the basic Arduino is really very little more than a manufacturer’s minimum setup – but the important thing is the volume of support software out there – in particular Ethernet software making it possible to create Internet-enabled devices such as my “EtherStat” Ethernet-and-infra-red-controlled unit which has now been on test for the past couple of weeks without a hitch and which will soon end up running Hollyberry Cottage.

None of the boards out there are without issue and so three of us collectively decided we’d have our own board and I took on the design job.

Armed with Eagle PCB package with which I’m well familiar (though I had some catching up to do) and a little imagination I set off putting this together from scratch -  I should at this time thank friends Jonathan and Aidan for the encouragement and also the latter for checking my work and generating the “Gerber” files etc.

The result – here it is..I nicknamed it ”UberBareBoard” as it has everything except the kitchen sink in it (feel  free to zoom in on any of these images which should expand or “lightbox” if you click on them).

The board follows the same form factor as the original Arduino though that was only by chance as I spotted an open-source version of the board outline and connectors. Having put several commercial boards together into various test projects, I came across the same problems every time – not enough power connectors, regulator getting hot, parts too close together, same pins used multiple times- and so what you see here is fairly simple but with sufficient extra pins to make life easy for lash-ups.

In the bare-board image above you’ll see on the front-left a 10-way connector – that’s for the cheap Chinese radio boards. Lower left there’s a 6-way connection – that’s pretty standard as are the outer connectors giving access to the 19 I/O pins and power and ground. Note top left the regulator is mounted flat on plenty of copper board (both sides) to dissipate heat and there’s room for a standard power connector (standard that is unless you’re Maplins who have a HOPELESS and hopelessly over-priced selection of connectors).

At this point it’s probably better to look at the populated board. Front right you’ll see a LED which is attached to D13, a far better place than making a power led as you can see the board working on power up (it flickers). Over on the right I’ve left room for a 3-pin infra-red receiver and a LED to go with that. Top right is the reset button, left from there the standard programming connector and left again (ie upper middle) you’ll see a power (+5 and GND) connector and a 2-pin battery connector. Relevant diode and charge resistor are fitted. The empty socket is for a 24c256 chip (64K EEPROM) and centre front you’ll see 2 diodes, they’re to drop the 5v supply sufficiently to use with the radio or Ethernet modules.

Mass production? No, we scoured the web for cheap UK prototype suppliers and ended up sending off to China for a set of 10 prototypes at a reasonable price – somewhat over a fiver each – and this for fully tinned, masked, cut to size prototypes of production quality. I’ll be using these guys again – turnover was little over a week.

I’m happy to say that apart from not having sufficiently small 1k resistors to mount them horizontally (that’s what I get for using standard library parts and not checking) and getting the mounting hole layers wrong (hence no mounting holes, quickly corrected with a drill) the boards work perfectly – and I have lots of plans for them.

This article was written as a follow-up to the original cottage thermostat article – and the first follow-up to this is here – NRF24L01 transceiver and Arduino.