eagle1109
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So you mean I should put 2 caps at the input of the LM7805 ? 1 ceramic 100nF cap and 1 electrolytic 10uF ?They should be enough but making the capacitor at the input side of the LM7805 a parallel connection of 100nF (104) and 10uF would be better, especially if the power cables from the PSU are long.
Note that it will no longer work from a 5V supply because you need some extra 'overhead' to allow the LM7805 to work. You will need at least 7V and preferably 8V at it's input to get a stable 5V out.
Your other alternative would be to wire a 1W or more rated 5.6V Zener diode across the supply and add a fuse in series with the power cable. The fuse will blow before the voltage is high enough to kill the PIC.
when i need a capacitor, i generally buy more than i need for that project
and put the rest into "general stock"
this works well for the inexpensive caps
other than that, i collected a few "standard" values to start with
mostly X7R ceramics, 25V or 50V
1uF, 0.1uF, 0.22uF ...
capacitances because ???
voltages because i'm generally working at 24V or less
Normally, trainees should put around 7-8 volts, and even if anything go wrong; like, a short or overvoltage, and these situations are less likely to happen, then the LM7805 would burn.All looks good but be careful not to overheat the regulator by either feeding it too much voltage or drawing too much current from your board. It will dissipate (voltage drop * current) in Watts and without a heat sink the temperature will rise around 50C per Watt. The voltage drop is how much is between the input and output pin of the LM7805 so its (input voltage - 5) and the current is in Amps.
The important thing with the connecting wire is it should be multi-strand. The AWG number only defines the cross section of the copper but not how many strands are used to achieve that cross section. Single strand copper is prone to hardening as it flexes and will eventually snap, multi-strand still hardens but being made of many finer wires it is more flexible and if a strand breaks in a bundle, its neighbors bridge the gap.
Tinned copper is just copper that has a tin (solder) coating. Copper is prone to oxidizing, even inside a PVC coating and it is difficult to solder to without using corrosive flux. By coating it with tin which is less chemically reactive, the copper is protected and solder will bond to it easily.
Brian.
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