Harlequin 128 PSU

[the_antithesis]

I purchased a Harlequin 128 kit which is a clone of the ZX Spectrum 128k model. My question is the instructions say the whole board runs off 5v, but requires a 9v center negative power input. I am wondering if there is any reason I shouldn't just replace most of the power circuit with a micro USB plug and just use a phone charger, like a Raspberry Pi. It seems like it should work, but I feel like I'm missing something.

[1024MAK]

It depends on the requirements of the video circuitry. For example, SCART connections require a control voltage for the automatic switching control lines. 9V being the minimum. I can’t remember off the top of my head what voltage the colour encoding chip needs.
All the rest of the board runs off a single +5V supply.

Also please note that a ‘charger’ is not necessarily a regulated power supply. A Harlequin board if being powered by an external +5V supply needs a regulated +5V supply that has noise and ripple levels below 100mV and has good load and line regulation. The output voltage should be within 5% (4.75V to 5.25V). Although I recommend a tighter range of 4.85V to 5.15V if possible.

The intended purpose of a charger is to supply a device so that it can recharge a battery or cell, and its electronics then runs from the battery or cell.

Mark

[Alcoholics Anonymous]

I do believe the whole thing runs from 5V but that might depend on which version of the harlequin you have.

Besides the above, another thing to consider is that the 9V is connected directly to the expansion bus. Expansion bus devices can use the 9V. I don't think the harlequin is supplying +-12V on its expansion bus but if so there will be another regulator that generates that from 9V.

[the_antithesis]

Thank you for the replies.

The instructions say it is entirely 5v and that many vintage accessories will not work without the 9v/12v/etc. on the bus. There is a capacitor on the 5v rail, which I believe is a filter, so I populated it. That should smooth things out regardless of where I get the 5v.

I am thinking of adding an Adafruit PowerBoost and a lipo charger so I can put a battery in this thing and make it portable. A PowerBoost is set to 5.2v to deal with USB wire resistance and similar in DIY projects, but, I can put a diode on the input to knock it down a hair if necessary.