Internal AtariVox activated using channel select switch

[spspspsp]

I have been thinking about ways to internalize an AtariVox into my 2800 for a few months. A quick forum search shows that other people have had the same idea, including recently where one individual used an 8P2W switch to accomplish this.

 

There isn't space for mounting a switch like that in my Atari 2800 system, and I don't want to cut a hole in the case.

 

I came up with a way to electrically enable/disable an AtariVox mounted inside my case.

 

Reading the AtariVox dev docs, I saw that only pins 1-4 are used by the AtariVox for data (plus pins 7 and 8 for 5V and GND). I started wondering if I could re-purpose some sort of IC buffer or level translator with an enable pin as a switch. One difficulty is that the AtariVox uses both regular serial communication and I2C communication on its pins, and and most chips I could find would only say they work with one or the other. However, Adafruit sells this level translator board that they say works with both I2C and low-baud SPI communication, so I gave it a shot. 

 

And it worked great in tests! This is the schematic:

 

 

I have pins 1-4 of controller port 2 connected to lines 2-5 on the HV (5V in the schematic) side of the board, GND connected to line 1, and I use pin 6 as my "enable" pin. The LV (3V3 in the schematic) side of the board is connected to the corresponding pins of the AtariVox. To enable the AtariVox, I feed 5V to pin 6 on both sides of the board (I tied them together), and to disable the AtariVox I connect GND to both pin 6s. An important thing to note is that although this board is bi-directional, the HV and LV sides are not 100% equivalent. If you connect the console-side controller port 2 lines into the LV side pins, even if you GND pin 6, the system still recognizes a Savekey being plugged in (and in some games the controller starts glitching out). However, if the console-side controller port 2 lines are plugged into the HV side of the board, grounding HV pin 6 completely cuts off communication between the console and the AtariVox.

 

I removed the RF modulator in my 2800, because conveniently, the channel select switch toggles pin 5 into the RF modulator between GND and 5V to select one of the two channels. I have pin 6 on my board connected to pin 5 where the RF modulator used to be. Thus, switching between channel A and channel B enables or disables the AtariVox as I please.

 

I am happy I no longer have an awkward extension cable sticking out of the front of my machine, and I now mix the system audio and the AtariVox audio together inside my case, so connecting up the enhanced audio is much easier.

 

This is a picture from when I was testing the level shifter board:

 

Here is a picture of the AtariVox mounted to the inside of my 2800 case using double-sided tape (I hacked together an audio breakout cable, and used a Dupont connector to make connections to wires I soldered inside the board):

 

And here is my system before final assembly. I also have a UAV board installed, and while I will eventually move these circuits to a permanent board, in case I need to adjust anything or notice problems, for now everything lives on a miniature breadboard.

Edited May 4, 2020 by spspspsp

[Voxel]

Great work, thanks for sharing the information.

[+x=usr(1536)]

Necrobump for a couple of quick questions as I'm getting ready to install one of these in the 7800.  I realise that the OP hasn't been around since last Hallowe'en, but seeing as I have the Adafruit BSS138 board now sitting here on my desk, hopefully someone else has done this mod and can clear a couple of things up.

 

Firstly, if I'm reading things correctly, +5VDC should be pulled directly to pin 6 on both the HV and LV sides.  However, my understanding is that pin 6 on the HV side is a +5VDC input, with pin 6 on the LV side being a +3.3VDC output.  There don't appear to be diodes on either of those pins, so how safe is it to do this?  Or am I misunderstanding the instructions?

 

Secondly, I'm working under the assumption that on the HV side, it'll be OK to just pull wire straight back from the headers on the Adafruit board to the appropriate solder joints on the right joystick.  Is this correct?

 

For the switch, I'm planning on temporarily pulling wiring for a DPDT latching pushbutton through the rear vents.  The long-term plan is to eventually replace that with a capacitive switch so that the whole thing is a zero-drill installation - just tap the appropriate spot on the case and the Atarivox is enabled or disabled.

 

If all that goes well, I'll repeat the process on the Junior, but not until the UAV is in there and I have some idea of how much space there is to work with.