External power supply for Classic ][

[James Harland]

Hello everyone, 

I've been running my Classic ][ so far with power via the FTDI cable. Now I want to solder together the RP2040 VGA serial terminal, so I'll want to start running the machine off of the barrel jack. The multiple AC/DC adapter I have has a choice of 4.5 or 6v and centre positive or centre negative. I suppose I should go for the lower voltage, but I just want to confirm this, and to ask about the polarity.

Thanks and all the best,

James

[Spencer Owen]

Hi James,

Neither of those voltages will be suitable. The RC2014 needs a 5v supply.

The cheapest and easiest way to get this is with a USB wall wart that most people have surplus of from old mobile phones. USB to 5.5/2.1 Barrel Jack cables such as this https://www.ebay.co.uk/itm/305198934201 are pretty ubiquitous too.

Alternatively, if you fit a 7805 voltage regulator an the two required caps, then you can use a higher voltage adapter. The 7805 needs at least 2.5v operating overhead, so you'll need at least 7.5v going in to it for a stable 5v out.

The socket is centre positive.

Hope that helps

Spencer

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[Peter Onion]

In my experience (some years ago I should add) the multi-voltage ones aren't very well
regulated. And you WILL (*) eventually plug it in with the wrong voltage set and the
wrong polarity, and then poof !

I would recommend getting a 5V one with center +ve just for this purpose.

PeterO 

I have the long grey beard to know this will happen :-)

[James Harland]

Thank you Spencer and Peter - I will look into getting a dedicated 5V centre +ve adapter then! 

Apologies if I'm duplicating responses - I thought I'd written a response to each of you but they seem to have disappeared.

I also wanted to know what the jumpers are for on the RP2040 VGA adapter, and if it is possible to have the regular Serial I/O module plugged in at the same time as the RP2040 (and so be able to power things from there while using a monitor and keyboard via the RP2040)

[Spencer Owen]

Hi James,

The jumpers on the RP2040 VGA Module are for selecting if TX1/RX1 or TX2/RX2 are connected to the RP2040. On a Classic II you only have a single UART (TX1/RX1), so it is kind of a moot point. If you had an RC2014 Pro or one of the Zed machines with two UARTs then it is more likely that you'll want to choose one over the other.

The nature of the way that the serial connection works means that if you have two devices connected to the RX pin on the RC2014, neither of them will be able to talk to the RC2014. Both of those devices will be keeping the signal high when not sending data, so even if one of them is pulsing it low, the other will keep it high, so nothing will get through.  If you have some jumper cables, though, you could connect just the ground and 5v pins from the FTDI adapter to the serial module to power it though.

However, you can also use the USB C port on the RP2040 VGA Module to power the RC2014.

Spencer

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[James Harland]

Hi Spencer,

Ok thanks for explaning about the serial connections, and that's good to know about the USB C - that's all I'll need for now.

I haven't understood what the purpose of the SD card is.

Thanks again

James