Monday 6 August 2012

Arduino-based Audio Cable Tester

I love the Arduino platform - it makes it so quick and easy to get things done.

The local music school had a need to test a bunch of audio cables (1/4" and XLR) in a hurry in preparation for the annual students' concert.  Yes, it can be done with a multimeter but if you have lots of them to do this becomes very tedious very quickly.  Sounds like a job for an Arduino

It does XLRs also...

The work is all done by an Atmel Atmega mircocontroller

All of the development work is done in the Arduino environment.  Once it was all working I just transferred the microcontroller onto a piece of perfboard (so that I could reuse the Arduino board for my next project).  The connectors on the far-left of the board (connected to pins 1,2,3,7 and 8 ) allow the Arduino board to be used as a programmer (see That link explains how to configure the Arduino to use the built-in 8MHz RC clock in the Atmega so no external crystal is required (neither accuracy nor flat-out CPU speed are remotely important in this application).

I also stuck a normal ICSP connector on it so that it can be programmed using a normal programmer (bottom-left corner).  This is handy:  once the code was complete I was able to blow the Arduino boot-loader away so that the sketch starts immediately rather than after a pause.  The downside is that if I want to use an Arduino to program it again I need to reinstall the boot-loader (for which that ICSP header will be very useful !)

The source-code is posted here.  The comments in the code list the required connections.  I haven't bothered to draw a circuit-diagram but if anyone wants one just leave a note in the comments below and I will post it here.




Laptop Transport

I needed a better way to carry my laptop on my folding bike.  I used a backpack for a long time which works fine except on hot days (sweaty-back syndrome !).  I tried a handlebar mount (the excellent but expensive  Klickfix system) which also works well but it adversely affects the stability of a bike which is already a little on the twitchy side.  The bike has a carrier but it is so low down that my heel clips anything that overhangs its perimeter.  There had to be a better way.

My simple solution is to make an attachment for the carrier which will allow the laptop case to be mounted vertically without moving around.

The band around the laptop back is a strip of 40mm x 2mm aluminium which is attached to carrier

It works so well I did the same thing for the folding bike's big brother...

I worry a little about the laptop having the guts shaken out of it (its a very nice laptop !) so I use a folded-up and partially inflated tube to give it a little "suspension":

I hope someone finds this useful.  If you have thought of a better way to solve the same problem I'd love to hear from you.