HP97 The journey begins
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04-29-2019, 01:25 PM
Post: #65
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RE: HP97 The journey begins
(04-29-2019 11:56 AM)Harald Wrote: I can see an inductor on your PCB. Presumably you are generating a voltage you need by means of a switched mode power supply. It might be a long shot, but is it possible noise from your power supply is causing the trouble? Have you tried shutting it down and supplying the circuit from a bench power supply? Hi Harald, I was musing that today in my doldrums. The wave forms look good, but there might be some unseen hash, spikes or radiation that's upsetting the works. I thought that having an unshielded coil right near the data path for the card reader might be an issue. A toroid might be better although for me this is hard to quantify. I looked into capacitive voltage boost chips which are much simpler to implement, but not deep enough as I only found ones with low mA outputs. Maxim look like they have some better ones. Most of the calculator operating power comes directly from the battery anyway. I will breadboard a linear power supply in the coming days and see how it goes. It needs the 3 mentioned voltages to run properly. It would be good if the HP card and display chips ran on 5.0 - 5.5 volts instead of the 6.2 - perhaps they do and are only running that high to interface to the PMOS logic. Thanks for the offer :-) cheers Tony |
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