I used an 08M Picaxe and a LM386 audio amplifier for the sound system. As there is no cam to drive the chuff rate I decided to use a Picaxe to generate the chuffs, based on the motor voltage.
I designed a SIMPLE voltage controlled, volume control to turn the white noise from the picaxe into a ?shaped? chuff. As well, loud or soft volume can be selected by a 3rd stick control on the 2.4 GHz transmitter which the picaxe decodes during the off time of the chuff.
I also decided to use a 4.7 ohm resistor in series with the motor to give more speed variation under load.
Having that resistor in circuit enabled me to use 2 voltage inputs to the picaxe, measuring voltage across this resistor and to calculate the armature current. Then I can calculate the actual armature voltage and thus true speed. I?m pleased with the result. Maybe that can be the subject of another topic.
Here?s the sound board viewed from under the footplate?
These pics shows the speaker in the rear of the cab and the driver and firebox ? I must give him a regulator handle soon !
I?ve now put on the vinyl lettering from G-ScaleGraphics (thanks Del ). I bought lining too, but have decided it?s got enough colour now.
So here?s some final pictures:
And a couple of short videos so you can hear the sound.
1st video (before final lettering) at?
http://youtu.be/-IPiawNAA68
comparison of sound systems at?
http://youtu.be/9azbwHli1ow