1 Jun 2014

Blasting wire tester project

I have been working on a new project for the last weeks. One of my friend is an electrical technician in a gold mine and regularly test blasting wire used to detonate dynamite. Sometimes, the wire is damaged, either open or short-circuited and he have to find where the problem is. He asked me if it was possible to create a simple portable device that continuously make a electrical contact for 1 second and release it for 1 second.

The challenge is quite easy: configure a 555 timer in the astable mode and wire the ouput to a relay coil and power all that with a 9V battery. However, I wanted to have something that looks nice and is robust so it needed a little effort on my part as my project are mostly programming and electronics.

The circuit

This time again I used Diptrace to design the schematic and PCB of my project. Before doing the PCB I tested the functionality of my circuit on a breadboard. The 555 timer is good to work from 5V to 16V and can source 200mA with its output pin, which is more than enough to drive my small relay. 

The circuit is pretty straightforward, I have a switch to connect the 9V battery to the circuit and I use a green "Power Good" LED and a red LED that flashes as the contact relay closes and open. The timing of the 555 is done with the 10uF capacitor (C2) and the 1k and 100k resistors (R4, R3). Below are pictures of the Printed Circuit Board.

The hardware

All the components used in the circuit have been bought on Tayda Electronics website, my favorite part supplier. I bought an aluminum case on Tayda to put the circuit in it and I wanted to have the top of the case look great, so I made a drawing on Inkscape and asked a local store to print a sticker out of it. Below is the original artwork:

I adjusted the DPI and size of the frame in Inkscape so I have a printed drawing the right size (2.4"x4.5"). The two following pictures are the sticker and the aluminum case with the sticker on it.

Once the sticker in place, I used a step drill bit (see picture below) to make holes the right size to put my LED holders and switch. The LED are held in place with a bezel panel mounting clip.

Video demonstration

If you want to hear the relay click and the red LED flash, just take a look at this YouTube video

That's it! I really like the outcome of this little project, this make me wants to do a lot more of good looking prototype put into cases :)

See you soon,


  1. Beau design Frédérick. Where did you get the PCB made?

    1. With OSH Park ( https://oshpark.com/ ). They come in pack of 3 and these one cost 4$ each :)

  2. Nice job Fred, on s'est vu au Maine
    Ca va?

    1. Salut Abdel, tu es bien le gars d'optimisation chez Comact, c'est ça?
      Oui ça va bien, envoie moi un courriel à fred_blais5(at)hotmail.com