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Neotron-Compute / Neotron-32-Hardware

Hardware design for the computer formerly known as The Monotron
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VGA amplifier #17

Open thejpster opened 4 years ago

thejpster commented 4 years ago

The TM4C can't really deliver enough current to drive 0.7V into 75 ohms. It can just about manage 0.6V into 75 ohms, but this is a little dim and pushing the GPIO outputs very hard.

We should add a transistor buffer, an 74-series buffer, or a proper analog VGA amplifier.

The SN74LVC244A might work, as a digital buffer. You'd put a potential divider on the output to get the 1.4V you need.

The AD8044ANZ three channel video amplifier would be perfect, but it's £8.91.

The MAX4395 is much cheaper at £1.83, but it's surface mount.

thejpster commented 4 years ago

The THS7314 is what all the Retro RGB adaptors do. As SCART is basically like VGA (but half the vertical resolution), it should do the trick? Only 70p a unit, but comes as a SOIC.

https://www.retrorgb.com/thsamps.html

https://www.digikey.co.uk/product-detail/en/texas-instruments/THS7316DR/296-26684-1-ND/2255104

thejpster commented 4 years ago

The 3PEAK TPF133A-SR is a 36 MHz 3-channel video reconstruction filter and 75 ohm line driver. It costs $0.16 from LCSC. 36 MHz video bandwidth is OK for up to a 72 MHz pixel clock.

https://datasheet.lcsc.com/szlcsc/3PEAK-TPF133A-SR_C155446.pdf

thejpster commented 3 years ago

Suggest we copy the design from the Neotron Pico.