Some months ago I built a simple wireless device to monitor temperature inside our household composting unit. Although the device worked initially well, I noticed two problems as time passed. First, the battery life wasn’t what I supposed it should be based on device data sheet and my measurements. Second, somehow moisture got into device no matter how well I tried to seal it with silicone. Continue reading “Compost Monitoring V2”
Heater circuit board
I decided to learn more about designing circuit boards with Eagle after reading an article about cheap chinese PCB manufacturer. Although there were some problems with their test boards the service is so cheap (about $1 for 5×5 cm board) that I wanted to try it.
For practice project I chose the pethouse heater described in previous blog. After spending some evenings with eagle I managed to produce required files to place an order at IteadStudio. The files were sent by e-mail and they confirmed that order was received. After that I didn’t got any messages from them, although I thought they were supposed to send some kind of shipping confirmation.
Anyway, after a few weeks I had a package at local post office. The board looks ok, but I noticed that I made some beginners mistakes (I should have read this before sending board to manufacturing) with my design when I started soldering parts to it. The bottom of board is filled with copper (a ground plane) but the isolation between solder pads is very small. As I forgot to specify it’s width the minimum from design rules was used (6 mils). Another mistake with ground plane was that I used thermals on high-current solder pads also. I had to remove solder mask around those pads and fill the gap with solder in order to be able to pass required current (about 6 A).
No other problems (none with manufacturing), so I replaced the prototype board on heater with this one and the system still works 🙂
The minimum order was 10 boards, costing a little more than $10 with shipping. Now I have extra 9 boards for future PWM controller projects!
Pethouse heater PWM
Our kids have two pet rabbits, which live in their own pethouse. To keep the house nicely warm and dry during winter I have installed a heater in it. Although the heater was originally designed for doghouses, but works very well here too. It has a simple plywood plate which contains an embedded resistor that provides about 40 W of heating power. System is powered with waterproof IP68 power supply which outputs 12 AC.
When the winter came again and I turned the heater on I soon got an alarm from my Blitzortung station that it no longer sends signals. When I looked at the station I found out that it was in interference mode, which means that system has detected some kind of electromagnetic noise near it. I didn’t first understand that it was the rabbithouse heater that generated the noise. Continue reading “Pethouse heater PWM”
Development versions of Pico]OS ports
I have been maintaining ports of Pico]OS for arm7tdmi, Arm Cortex-M, Texas Instruments MSP430 and unix. Arm7tdmi is mainly for Philips/NXP LPC2xxx series, although there are other, untested cpu families in that port. These ports are included in recent official Pico]OS downloads. Continue reading “Development versions of Pico]OS ports”