Harmony Cart Interference

[Mr SQL]

On 2/22/2016 at 9:16 PM, Monk said:

After some more extensive testing, it looks like the interference is not as bad as it was previously. I can hardly notice it in many games, and in some that I can notice it in, it's not that distracting after all. Sometimes I really have to try hard to be able to see the interference (depending on the game), and in other games, it forms a different pattern, that somehow fits the game graphics nicely.

 

So I decided not to try to open up the Harmony Cart or do any aluminium folio-modifications to the Atari 2600 jr., I mean - the pixels can still be seen clearly and the games are still awesome and atmospheric, so it doesn't matter all that much. Plus, when I concentrate on the game and the atmosphere, sound and graphics, I often forget that the interference even exists at all.

 

The few games that really display the interference in an almost distracting way (Pitfall!, for example), can always be purchased as separate cartridges anyway. Atari 2600 jr. is a wonderful, magical machine, and Harmony Cart complements it perfectly!

 

Old games benefit from CRT televisions, and interference often goes together with RF signals, so it just adds to the charm in a way that a modern TFT-lifestyle cannot emulate. So what's a little interference every now and then in a few games.. just added charm, basically.

Old discussion but I played some of the games that show the vertical interference bars on the Uno cart and the video was crystal clear with no vertical bars, just like the SuperCharger. 

 

Interesting whatever is causing the degaussing issue; maybe something isn't hitting ground or a tiny Faraday cage could be necessary to construct if the ARM is stepping up to cause the interference through a harmonic - not all games have the interference bars, which is part of the puzzle. I had really noticed the difference playing Atlas in the DOT games collection - that's a cool port of the 80's classic Catalyst for the CoCo that I had initially thought was an original.

 

[+batari]

I suspect the interference is worse on old Harmony carts. The original carts used a two-board design and didn't have the ground plane on the PCB that current carts have.

 

If anyone has interference with a newer Harmony cart, though, it might be due to the isolation circuit for the USB port power, as the USB port can also power the cart. This is done using a common cathode dual-diode so you can plug USB in while the cart is in the console, and not only will nothing will be fried in the cart or console if anyone did this, it can also be useful. During development we basically used the Harmony as a logic analyzer and sent data out the USB port for debugging purposes.

 

To help support this theory, I have seen the same sort of interference reported with Atari's 32-in-1 cart. This cart has a diode in it, possibly indicating the potential source. I could eliminate the diodes of course, but I think the dual-power ability, and potentially the ability to use a Harmony as a logic analyzer for debugging a game, as we did, is more valuable )

 

In any case, with my own testing, I can eliminate RF interference with good cabling, particularly a quality cable that comes with a ferrite choke, or if a cable doesn't have one, use one of the clip-on chokes from another cable. I have even had success with just running the cable through a ferrite ring a couple of times.

 

As the UNOcart lacks a USB port and the Supercharger doesn't have anything analogous to that, of course neither would have any need for the power isolation circuitry.

[Mr SQL]

5 hours ago, batari said:

I suspect the interference is worse on old Harmony carts. The original carts used a two-board design and didn't have the ground plane on the PCB that current carts have.

 

If anyone has interference with a newer Harmony cart, though, it might be due to the isolation circuit for the USB port power, as the USB port can also power the cart. This is done using a common cathode dual-diode so you can plug USB in while the cart is in the console, and not only will nothing will be fried in the cart or console if anyone did this, it can also be useful. During development we basically used the Harmony as a logic analyzer and sent data out the USB port for debugging purposes.

 

To help support this theory, I have seen the same sort of interference reported with Atari's 32-in-1 cart. This cart has a diode in it, possibly indicating the potential source. I could eliminate the diodes of course, but I think the dual-power ability, and potentially the ability to use a Harmony as a logic analyzer for debugging a game, as we did, is more valuable )

 

In any case, with my own testing, I can eliminate RF interference with good cabling, particularly a quality cable that comes with a ferrite choke, or if a cable doesn't have one, use one of the clip-on chokes from another cable. I have even had success with just running the cable through a ferrite ring a couple of times.

 

As the UNOcart lacks a USB port and the Supercharger doesn't have anything analogous to that, of course neither would have any need for the power isolation circuitry.

Very cool this is gone on the new carts - my Harmony is from 2011 and still works great btw!

 

I do have two ferrite chokes that are pretty big on the RF cable and everything is crystal clear with many games having no vertical bars present, but some games like the Atlas homebrew always have them. 

 

I upgraded to the Uno over the Encore because I wanted to play Andrew's Chess but was pleasantly suprised at the clean video on the games that had the bars on the Harmony.

 

Really curious what could possibly be different when those specific games run that cause the interference -

 

The logic analyzer is awesome functionality, could those games somehow be activating the function to send data through the USB port on the earlier model to selectively trigger the interference?