21-09-2016, 04:14 PM
Hi All
This is my attempt at building David Robinson's System A modulator which covers all 13 Channels. I found the original threads on the UKVRR which 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

This is my attempt at building David Robinson's System A modulator which covers all 13 Channels. I found the original threads on the UKVRR which 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