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Posts posted by Enrico

  1. I've built one too.

    But since i discovered Hydrogen Peroxide + Muriatic Acid, i just don't use it anymore.
    You can find (at least here in italy) Hydrogen Peroxide 40% vol from airdressers, it is present in the products they use to make air shiny blonde.

    I just lay the pcb in the plastic box and cover it with a small amount of muriatic acid (just enough to cover the pcb), then i squirt a small amount of air product and wait around 10 minutes, less if you give it a little shake sometimes.

    I agree that this solution is far more dangerous than using ferric cloride, but if the right precautions are taken, you save a lot of money:

    - No pcb tank nedeed, just a little plastic box (the mixture i mentioned above is very powerful in very little quantity)
    - 10 minutes maximum etching time, even for large pcbs, i had perfect results in less than 10 minutes without eating nor shaking.

  2. During the process of building my own dual-variable power supply, I decided to mount a cooling fan, controlled by a lm35 temperature sensor, to cool off the heat produced by the numerous of components.

    Inside my box (old ammo case from WW2) there is very little space:

    - 2 backlit displays (2x16 char)
    - 1 Toroidal transformer 50 VA
    - 1 Toroidal transformer 225 VA
    - A total of 4 "TO220" voltage regulators (2x 7805, 1x 7905, 1x 7812) each one with it's fellow heatsink.
    - A big heatsink where 2 LM338TK  (TO3) are mounted, this heatsink is mounted partly inside the case, partly outside.

    I placed a 120 mm cooling fan driven by a PIC - LM35 based system.

    My question is:

    Where is the correct and most efficient place to put the LM35 sensor?

    I thought about the big heatsink, but it will be tiepid most of the time, because of its size and the fact that it is, in part, outside the case.

    I thought about the 220 VA Toroidal transformer, it should produce some heat under load.

    I even noticed that the various LM7xx that populates my utility pcbs are often very warm (especially the lm7805 that powers the two displays, 3 pic and some leds).

    I couldn't give myself a satisfying answer

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