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Old 21st Sep 2016, 5:24 pm   #1
FRANK.C
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Join Date: Feb 2006
Location: Roscommon, Ireland
Posts: 605
Default David Robinson's System A modulator

Hi All
This is my attempt at building David Robinson's System A modulator which covers all 13 Channels. The original threads are here and here

Both Audio and Vision modulators are the same as David's. The only change that I made was to simplify the audio input as I don't need the separation between left and right channels that David did. There was some debate about whether the 3.5 MHz filter was necessary or not. I decided to keep it, the coil the David used is no longer available, I used a 'Mini Mod' transformer in it's place and it works quite well.

I have made some changes to the Microcontroller side of things. I am using a 18F1330 Microcontroller. The I2C buses for the two modulators now share a common clock. The microcontroler produces a very basic test card and an audio tone of approximately 300Hz which are fed to the modulators via switched phono plugs. When a Video or Audio plug is inserted into a Phono socket the test card or audio tone is disconnected.

I made a PCB for it which made assembly of the SMD's much easier. The PCB is double sided with one side used solely as a ground plane. The PCB was produced using the laser printer method which left the copper pitted but it is still acceptable.

Frank
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