A8PicoCart - UnoCart on a Raspberry Pi Pico

[Piotr D. Kaczorowski]

@E474,

 

Masterpiece

[E474]

Hi,

 

  Can I ask for a bit of help from the more "electrically" knowledgeable members regarding an extension to the PicoCart. I want to avoid damaging the 8-bit's Freddy chip, or causing other issues, I know this can be a problem if power comes in to the PicoCart from another source, but I don't have the knowledge to work around it.

 

  In summary: the Purple Pico has 2 unused GPIO pins (A2 and A3), and I thought they could be connected to a Pico W (essentially via a UART, either by shuffling the connections on the PCB, and changing the pins used in atari_cart.c, or emulating a UART using PIO - see https://www.joshka.net/2022/11/pio-for-midi-with-raspberry-pi-pico among other places for an example of a UART implemented on arbitrary pins using PIO).

 

  This would mean a cartridge with both a Purple Pico and a Pico W on it.

 

  The Pico W could be used to:

 

    - drive an SIO connection, so serving ATR/ATX images

    - drive a DVI/HDMI output for 80 column mode, etc

    - provide Wifi connectivity, as in FujiNet

    - provide a microSD card connection via SPI

    - expose the unused GPIO ports as header pins for other I/O

 

  This would mean building something like a PicoCart Duo (working name), with a Purple Pico handling cartridge bus I/O, and the Pico W handling all other I/O, and the Picos communicating with each other via UART (unless there is something better to use).

 

  I figure if I hook everything up including the +5V line on the SIO bus, it's sure to fry the Freddie if I plug it into a powered 1050 when the 800XL is off, but is there a simple fix for this? 

 

  A few pictures (below) to show how things are intended to be organised, but not wiring anything up before I know I won't break anything!

 

   Not sure if the guys from team FujiNet, e.g. @mozzwald, @tschak909, @apc have an opinion on this, or if others who have commented on the hardware issues in this thread, e.g. @mytek, @Piotr D. Kaczorowski, @ijor or @electrotrains have an opinion too? One thing to throw into this is that although the FujiNet hardware is based around an ESP32, the advantage of the Purple Pico/Pico W is that it doesn't use surface mount components, so the PCBs are easy for the less skilled solderers like myself to make up.

 

   Comments/opinions?

[mozzwald]

51 minutes ago, E474 said:

I figure if I hook everything up including the +5V line on the SIO bus, it's sure to fry the Freddie if I plug it into a powered 1050 when the 800XL is off, but is there a simple fix for this? 

I think you need to give a little more info. Why do you need to hookup SIO 5V? Can you power both Picos from the same 5V?

[Piotr D. Kaczorowski]

@E474,

 

Several people are working on some solutions that will soon be published. You certainly have interesting ideas. However, I don't know why Freddie would be the one to get damaged specifically. You could probably damage various other things as well. As for power separation, this topic has already been preliminarily discussed. You can also look at the Fujinet schematics to see how external power has been handled, which is needed for Fujinet in the case of the 1200XL, where there is no power on the SIO.

[E474]

On 8/28/2023 at 7:10 AM, electrotrains said:

The aim of the project was to make an easy to assemble and very inexpensive multicart with minimal components. Others are free to improve the design at the cost of complexity of build...

 

Having said that, I did consider adding the diode - but I'm not sure that the diode alone will offer complete protection...

 

I managed to kill my 65XE early in my cartridge experiments by powering up a DIY cartridge before powering up the Atari - even though 5V was not connected to the cartridge port. Enough power was supplied from the cartridge through RD4/RD5 to fry the Atari MMU.

 

So powering up the Pico board (by USB) when plugged into an Atari - even if the diode on 5V is added - still has the potential to damage the Atari if any of the GPIO pins on the Pico are not in high impedence (input) mode.

 

(At the moment the firmware decides to go into cartridge mode if it detects the atari clock signal on an input pin within 100ms after boot. Otherwise it goes into USB mass storage mode.)

 

Any thoughts mytek?

 

 

 

 

Hi @Piotr D. Kaczorowski,

 

   It was this comment - I'm assuming that if you hooked up the SIO bus to the Pico W, you would have to hook up the +5V SIO line to the VSYS pin on the Pico W (which would be also connected up to the VSYS pin on the Purple Pico, and the +5V line on the cartridge port - I'm really not clear on whether the +5V SIO line actually needs to be connected up though. I assume SIO ground would absolutely have to be connected though. Unfortunately I have a fairly week grasp of the hardware/electrical side of things.

 

[E474]

14 minutes ago, mozzwald said:

I think you need to give a little more info. Why do you need to hookup SIO 5V? Can you power both Picos from the same 5V?

Hi @mozzwald,

 

   The idea is to use the second Pico (the Pico W) to drive the SIO bus, I assume you would need to hook up the +5V SIO line to the Pico (not sure of this though). I think the Ultimate Cart also drives the SIO bus, so the idea would be the same as this.

[Piotr D. Kaczorowski]

1 minute ago, E474 said:

Hi @Piotr D. Kaczorowski,

 

   It was this comment - I'm assuming that if you hooked up the SIO bus to the Pico W, you would have to hook up the +5V SIO line to the VSYS pin on the Pico W (which would be also connected up to the VSYS pin on the Purple Pico, and the +5V line on the cartridge port - I'm really not clear on whether the +5V SIO line actually needs to be connected up though. I assume SIO ground would absolutely have to be connected though. Unfortunately I have a fairly week grasp of the hardware/electrical side of things.

 

 

I guess I don't know what you want to do. After all, you already have power and ground on the cartridge. If you start connecting these things additionally, you will certainly get what is known as a ground loop, which may increase noise.

 

[E474]

1 minute ago, Piotr D. Kaczorowski said:

 

I guess I don't know what you want to do. After all, you already have power and ground on the cartridge. If you start connecting these things additionally, you will certainly get what is known as a ground loop, which may increase noise.

 

 

Basically I would like to have the same SIO connector that the Ultimate cart has. However, I'm not sure how to wire up the SIO bus to the Pico W without having power going back in to the 8-bit when the SIO cable is plugged in to the back of a powered up 1050, and the 800XL is off (and the PicoCart Duo is plugged in to the 800XL).

 

[Piotr D. Kaczorowski]

2 minutes ago, E474 said:

The idea is to use the second Pico (the Pico W) to drive the SIO bus, I assume you would need to hook up the +5V SIO line to the Pico (not sure of this though).

 

You should connect it to the same +5V source from the cartridge port. If you wish to add extra stability, you could include an additional 220uF capacitor on the +5V line.

 

 

2 minutes ago, E474 said:

I think the Ultimate Cart also drives the SIO bus, so the idea would be the same as this.

 

AVG Cart ?

 

[mozzwald]

Just now, E474 said:

 

Basically I would like to have the same SIO connector that the Ultimate cart has. However, I'm not sure how to wire up the SIO bus to the Pico W without having power going back in to the 8-bit when the SIO cable is plugged in to the back of a powered up 1050, and the 800XL is off (and the PicoCart Duo is plugged in to the 800XL).

 

what ever powers the first pico can power the second one, provided there is enough current available from the atari (or external if you're using it). There is no need for the SIO 5V line specifically. On Fujinet, it's only used for power, but does not need to be.

[Piotr D. Kaczorowski]

@E474,

 

 

As you know, we are just a front-end interface for ChatGPT-4. :))))

 

 

[E474]

Hi,

 

   Yes, I meant the AVG cart.

 

   What wasn't clear was how to wire up the SIO connector to the Pico W. I didn't want to get in to the situation where the Pico was powered by the +5V cartridge line, but also connected to the +5V SIO line, as power would be flowing along this line (from the powered up 1050) when the 800XL was powered down. However, if it's not necessary to connect up the SIO +5V line to the Pico (thanks @mozzwald), then I only need to connect up the SIO lines: Data In, Data Out, GND and Command.

 

   

[electrotrains]

I did a new version of the PCB last weekend which has the purple pico rotated by 90 degrees with the USB pointed downwards towards the cartridge port. My new boards shipped from China this morning, so I expect to have them in a week or so. Assuming they work fine, I'll post the new version of the PCB & gerber files on github, along with new STL files for the 3d printed shell.

 

So if you were planning to get PCBs made, you might want to hold off for a week or so.

 

(For those that haven't read the whole thread, the reason for this redesign is to physically prevent USB connection when the cartridge is plugged into the Atari. That removes the need for any extra components to protect the atari in the event that the device gets power through USB while connected to an unpowered Atari, and keeps it a simple and cheap build.)

 

Robin

Edited September 8, 2023 by electrotrains
typo

[Piotr D. Kaczorowski]

1 hour ago, electrotrains said:

I did a new version of the PCB last weekend which has the purple pico rotated by 90 degrees with the USB pointed downwards towards the cartridge port. My new boards shipped from China this morning, so I expect to have them in a week or so. Assuming they work fine, I'll post the new version of the PCB & gerber files on github, along with new STL files for the 3d printed shell.

 

So if you were planning to get PCBs made, you might want to hold off for a week or so.

 

(For those that haven't read the whole thread, the reason for this redesign is to physically prevent USB connection when the cartridge is plugged into the Atari. That removes the need for any extra components to protect the atari in the event that the device gets power through USB while connected to an unpowered Atari, and keeps it a simple and cheap build.)

 

Robin

 

 

So maybe I have my tiny contribution It's great that it has been taken into account.

 

 

[electrotrains]

9 minutes ago, Piotr D. Kaczorowski said:

 

So maybe I have my tiny contribution It's great that it has been taken into account.

 

 

Yes, thanks to you and @_The Doctor__ for the suggestion!

Edited September 8, 2023 by electrotrains

[+mytek]

5 hours ago, electrotrains said:

I did a new version of the PCB last weekend which has the purple pico rotated by 90 degrees with the USB pointed downwards towards the cartridge port. My new boards shipped from China this morning, so I expect to have them in a week or so. Assuming they work fine, I'll post the new version of the PCB & gerber files on github, along with new STL files for the 3d printed shell.

 

So if you were planning to get PCBs made, you might want to hold off for a week or so.

 

(For those that haven't read the whole thread, the reason for this redesign is to physically prevent USB connection when the cartridge is plugged into the Atari. That removes the need for any extra components to protect the atari in the event that the device gets power through USB while connected to an unpowered Atari, and keeps it a simple and cheap build.)

 

Robin

And I have my 4-in-1 daughter boards for the 576NUC+ coming from China (just shipped today). These not only incorporate the A8Pico cart, but also an untested protection circuit that should allow safe access to the USB under any condition. If all goes well, I'll post an updated schematic of the A8Pico Cart aspect incorporating this protection circuit. No cartridge version PCB gerbers will go along with this, but anyone that wishes to do so can create a new cartridge board based upon it.

[The Mr. Video]

Got my Purple Pi Eater in today. Now I need to get a cartridge board to put it in. Where did you guys order your PCBs?

[ascrnet]

Hi all,

 

On my side I already started adding those rare cartridge types that I would like to emulate.

 

Thanks to @electrotrains for sharing his work I added 3 more which are:

• 5 - DB 32 KB cartridge
• 39 - Phoenix 8 KB cartridge
• 57 - Standard 2 KB cartridge

a8_pico_cart_b03.uf2

If you want to try it they are in the github or if you have others much better. 😉   regards

[bfollowell]

1 hour ago, The Mr. Video said:

Got my Purple Pi Eater in today. Now I need to get a cartridge board to put it in. Where did you guys order your PCBs?

I ordered mine from PCBWay. I have ten coming in if you'd like to purchase one is mine. Otherwise, their minimum order is five.

 

[bfollowell]

Well, my Pico clone cards and switches arrived. Now I just need to wait for my PCBs to get here.

 

[+mytek]

My boards are coming today

 

They're a little more complex than just the Cart version, and incorporate a protection circuit that I am hoping proves to be fool-proof (just gotta find a fool to test it ).

 

 

I changed my mind on having an independent switch to disable the A8Pico Cart aspect, since pressing 'X' does just that.

[bfollowell]

My original A8PicoCart PCBs arrived from PCBWay today. I'd ordered ten but wound up with an extra one. I have enough boards, Pico clones and switches to make ten uncased A8PicoCarts. Anyone not wishing to order a lot of extra boards and supplies from China is welcome to PM me. You can easily print your own cases or have them printed and mailed to you from an online printer like I'll do. After mine, I'll have enough stuff to make nine extra full carts, plus an extra PCB. I'll be glad to work out pricing for component cost and shipping. Just PM me, don't reply to this thread.

 

[Piotr D. Kaczorowski]

A bit off-topic, but I've noticed that UltimateCart has returned to the market.

 

https://www.ebay.com/itm/115911490326

[Piotr D. Kaczorowski]

@electrotrains,

 

How much does the hardware handling differ between UnoCart and UltimateCart? Could UltimateCart be made based on Pico?

[Wrathchild]

16 minutes ago, Piotr D. Kaczorowski said:

How much does the hardware handling differ between UnoCart and UltimateCart?

Completely different processors:
https://github.com/robinhedwards/UltimateCart
https://github.com/robinhedwards/UnoCart