This might be a stupid question but... if the external power supply was up to it, could 5v power be drawn from inside the ZX81 to power the Pi zero with the display mod? - https://www.sellmyretro.com/offer/details/63615
Reason I'm asking, is because I've built the mechanical keyboard and I'll have to make a new case. If I can put the Pi Zero inside the case and power the whole thing from one input, I can make things nice and self contained.
Grateful for thoughts.
Possible to run Pi from inside Zeddy?
Possible to run Pi from inside Zeddy?
All that I've learned - https://msknight.com/bbc/index.html#zx81
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1024MAK
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Re: Possible to run Pi from inside Zeddy?
It's not recommended to run anything that uses any significant power from the ZX81's 5V supply if using the original 7805 voltage regulator.
And a Pi counts as needing a significant amount of power. Plus the RGBTOHDMI - HDMI circuitry needs power.
Although the 7805 voltage regulator is rated for 1A, the standard metal heatsink is not suitable for handling any significant extra loads. A much bigger heatsink would need to be provided. In practice, this means relocating the 7805. The heatsink would 'generate' more heat as well, not good if it's mounted inside a case.
Even if the limitations of the 5V were not a problem, the most common ZX81 mains power supply unit (PSU type UK700) is only rated at 700mA (0.7A). A standard ZX81 uses between 350mA and 400mA (typical, the exact amount depends on which makes/types of chips are used). Leaving only 300mA to 350mA spare. And you don't really want to max out any PSU.
Even the higher rated UK1200 is not particularly good. Although rated by Sinclair at 1200mA (1.2A), from the construction, I get the impression that's it's short term maximum rating (also known as 'tool' rating) not it's maximum continuous current rating.
So I would power the RGBTOHDMI - HDMI and Pi separately to the ZX81.
Before I can offer any other suggestions, I need to know what, if any expansions you are thinking about or intending to use with your ZX81. Such as are you going to use a RAM pack? As that then determines what other options are available.
Mark
And a Pi counts as needing a significant amount of power. Plus the RGBTOHDMI - HDMI circuitry needs power.
Although the 7805 voltage regulator is rated for 1A, the standard metal heatsink is not suitable for handling any significant extra loads. A much bigger heatsink would need to be provided. In practice, this means relocating the 7805. The heatsink would 'generate' more heat as well, not good if it's mounted inside a case.
Even if the limitations of the 5V were not a problem, the most common ZX81 mains power supply unit (PSU type UK700) is only rated at 700mA (0.7A). A standard ZX81 uses between 350mA and 400mA (typical, the exact amount depends on which makes/types of chips are used). Leaving only 300mA to 350mA spare. And you don't really want to max out any PSU.
Even the higher rated UK1200 is not particularly good. Although rated by Sinclair at 1200mA (1.2A), from the construction, I get the impression that's it's short term maximum rating (also known as 'tool' rating) not it's maximum continuous current rating.
So I would power the RGBTOHDMI - HDMI and Pi separately to the ZX81.
Before I can offer any other suggestions, I need to know what, if any expansions you are thinking about or intending to use with your ZX81. Such as are you going to use a RAM pack? As that then determines what other options are available.
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.