Double sided PCBs – aligning the sides for exposure

Jig for aligning mask for double sided pcb

Getting the two sides of an exposure mask to align well when making a two sided PCB is always a pain. With a simple cardboard jig it becomes easier. Quite surprisingly I have not seen this idea anywhere. The usual advise is to make a pouch of the two sides of the mask, but that does not help much when you need to turn the pcb around to expose the second side. Continue reading Double sided PCBs – aligning the sides for exposure

DIY home PCB exposure and etching process

etched_pcbIt looks like my diy pcb manufacturing process is working reasonably well, so it’s time to share what I have learned. This covers printing an exposure mask, exposing, developing, etching and drilling/cutting – all the way to a finished pcb. My process is an extremely low-cost one, with minimal tools and supplies needed. The results are not perfect (more on that below), but very much adequate for my purposes, and covers all of my pcb making needs.

Creating an exposure mask

I am using regular office printing paper as the exposure mask. The paper is oiled after printing to make it translucent. Continue reading DIY home PCB exposure and etching process

PCB exposure timer with Picaxe microcontroller and LCD display

exposure_timerQuite appropriately, the first board that I exposed with my UV exposure box was a timer to control the exposure. The heart of the timer is a Picaxe 08M2 microcontroller. The timer has also an inexpensive 16×2 characters LCD display (based on a HD44780 controller protocol) and a rotary encoder to set the time. The rotary includes a push button that starts and stops the timer and the exposure. An I2C I/O expander chip PCF8574 interfaces the PICAXE to the display module to save i/o pins on the microcontroller. This way even a small 8-pin microcontroller can be used. Continue reading PCB exposure timer with Picaxe microcontroller and LCD display

Visual count down timer web application


I’ll post a software mini project for a change. My wife asked me the other day if I would know where she could download a count down timer application. She is a teacher, teaching first grade this year, and she needed a visual timekeeper for activities in her class. The idea was to display the timer on their fancy interactive whiteboard while the kids were working on something. This immediately sounded like a project to me.

 To cut things short, here are the links to the web  pages. Continue reading Visual count down timer web application

UV led pcb exposure box


One of the major hurdles when making printed circuit boards at home is to solve how to transfer the PCB design to a copper clad board so that the extra copper can then be etched away. You can print transparencies with your printer and you can get inexpensive photosensitive boards but you still need some source of ultraviolet light for transferring the design to the board. I found some inexpensive 5mm UV leds on eBay and decided to give this a try. Other people had reported success so I was confident that this would work. Of course this is a chicken-or-the-egg type of problem. You need to be able to expose one PCB in order to make a device that you can use to expose PCB’s. Luckily I had access to the tools required. You could also easily construct this on veroboard.

I had an old A4/letter size scanner that was no longer producing sharp scans. The top part with the bed and lid looked just perfect Continue reading UV led pcb exposure box

Submergible 12V swimming pool lights


In the wintertime the evenings get dark and therefore plunging in to the dark lake is not as pleasant as it is in the summer. Led lights to the rescue!

Above is a photo of the lights in a pool, or actually a hole in the ice in a lake.

Submergible led lights can be made with a car battery, a couple of 1 watt leds, a constant current driver, a piece of clear 1 inch diameter PVC hose and two small pieces of e.g. aluminum profile for led heatsinks. The leds Continue reading Submergible 12V swimming pool lights

Sound triggered glowing led eyes for Halloween


As we are getting close to Halloween, I’ll present this project I did last year. It is about  a pair of leds that will light up when there is a loud sound, such as a person raising her voice. The intensity of the leds will depend on the loudness. I used yellow leds as the eyes for a moose/elk antler trophy at my cottage. For this project, as for many others, I used a Picaxe 08M2 microcontroller. Picaxes are inexpensive, very simple to use, BASIC language programmable and Microchip Pic based, see You can do surprisingly much with them.

The project has two parts, a small board for the Picaxe and another for a sound sensor with condenser microphone, amplifier and peak detector. Continue reading Sound triggered glowing led eyes for Halloween

Variable voltage bench supply with current limiting


You will need some source of electrons for every project. It did not take long before I started to think about other power sources but the obvious batteries. My first power supply was a simple LM317 based one with a potentiometer to vary the output voltage. The one important feature that was missing was current limiting. I saw an old Elektor magazine article (Elektor 7-8/2008 p. 106) about a mini bench supply that seemed like just what I needed.

The schematic needed a little tweaking Continue reading Variable voltage bench supply with current limiting

Motion activated joule thief led bike light

Joule thief based bike led light installed on a bicycle.

I have been wanting to make something useful with the joule thief circuit design and some 1W star leds that I have. I found an old bicycle light that used a 0.5A 2.5V halogen bulb and two C size (LR14) batteries. It looked like it would be a good candidate to convert to led. I also wanted to create a light that would switch on automatically as the bike moves, and off again with a delay after the bike stops moving. In other words a motion sensor activated light that I would not need to switch on or off. That would Continue reading Motion activated joule thief led bike light