My latest project. Model 1 Expansion interface Power supply

[Chromedome45]

Built a power supply for my Expansion Interface. Why? Why not I did it for my TRS-80 itself. This one uses a Radio Shack 3 amp 12.6 volt transformer for the DC side (A little over kill could use a 1.2 amp the original idea was to power both the EI and the TRS-80. But for now only the EI) and a Radio Shack 12.6 volt 1.2 amp transformer for the AC side. Just followed the schematic at TRS-80.com a variation of the one that TRS-Ian and company built. This is actually my second home built power supplies. Both work fine. A cheapo solution in a way. I am in the process of writing a guide on how to do it if any one feels up to the challenge of trying it themselves. Costs about US$ 35.00 in parts at Radio Shack but could be done cheaper if ordered parts on line. Guide will be up sometime after the New Year.

And obviously these are 120V on the Primary side Transformers for US Canada power mains. Overseas users will need to obtain transformers of the 220 or 250 Volt variety. Just remember the secondary needs to be around 12.6 to 14.00 volts.

 

[Jimmy]

Frank:

Nice project, I will be interested in the guide.

Thanks,

Jimmy

 

[Chromedome45]

It is not really that hard. Look here at the schematics: http://www.trs-80.com/wordpress/zaps-patches-pokes-tips/zaps-model-i-power-supply/ scroll down till you see "build your own" As mentioned you can get the parts at Radio Shack. I used 2 12.6 volt 1.2 Amp Transfomers for my TRS-80.

 

[TRS-Ian]

Nice work, that's a great looking little power supply.. if you double up the output cable will there be enough reserve power in the system to power the Model 1 as well?

Some years ago (like 2 decades or more) I built a similar thing using two 240V transformers (what with being in Australia and all...) and I noticed significant screen shimmer with the two transformers in the EI so close to the monitor. Do you find a similar thing or do you still have a relatively stable screen image? I eventually tracked it down to being electrical noise generated by the two transformers, because when I moved my monitor away the screen shimmer settled down.

When Dean designed the toroid power supply I was keen to see if the same problem re-appeared and was pleased to see the toroid supplies are much more electrically quieter. This may not be a problem in the USA since the transformers you use are half the size of ours.

Nice work.

Ian.

 

[Chromedome45]

The original plan was to power both units. Which I may still do. Just need to get another Din cable. As for screen shimmer I haven't even hooked everything up yet. Guess I need to do that and see if I get the shimmer you mentioned. I will do that today and report back. Has me curios!


Ok plugged in the EI and the Model 1 no shimmering noticed. So for those in Europe and Australia, New Zealand and other countries using between 220-240 V Mains
power be aware of the problem Ian noticed in above post. Possible shimmering of screen. So maybe best to avoid doing this! But if you feel like trying by all means give it a shot.