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I am trying to download a program on to my PIC circuit. As you know the pic isn't supposed to operate with anything larger than 5v. I don't have any access to a battery pack which could hold 3 x AA batteries. What i do have are lods of other stuff, that may be useful. I was thinking that if i used two 330 ohm resistors to create a potential divider then had another battery snap going off from that to the pic circuit. Would that work?

Schematic of theory[![Bread board of theory]2

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  • \$\begingroup\$ Tape or rubberband 3 AA batteries (and some wires or bits of metal) together. Properly bent wires on a protoboard will do, too. Or wedge them into a suitable cardboard, wood or plastic box, or tube (tube may be easier as you don't ned to provide any inter-battery connections.) 9V has MUCH less capacity (amp-hours) than AA - so even if you use a switcher, you'll have comparatively poor runtime. Cost is usually worse, too. \$\endgroup\$
    – Ecnerwal
    Feb 14 '16 at 1:17
  • \$\begingroup\$ Why is this being voted negatively \$\endgroup\$ Feb 14 '16 at 18:06
  • \$\begingroup\$ Google "9V to 5V regulator cap". Or build your own. \$\endgroup\$
    – mckenzm
    Jun 21 '18 at 20:51
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That's not usually a good idea for a couple of reasons.

  • It wastes power. From \$ V = I \cdot R \$ we can calculate the current, \$ I = \frac {V}{R} = \frac {9~V}{660~Ω} = 13.6~mA \$ without doing anything useful!
  • More importantly, the voltage will vary depending on what the processor load is. If the PIC has a wide voltage tolerance you might get away with it.

You really need a voltage regulator.

A quick work-around is to use a USB port as power supply. Get a cheap USB cable or broken USB device, keep the A-plug end (that goes into your computer) and cut the plug or device off the other end. The red (+) and black (-) should give you a 5 V regulated and current-limited supply. Check with your multimeter.

USB cable pintout

Red   | Vcc (+5 V)     | Connect to circuit +
White | USB Data -     | Not used
Green | USB Data +     | Not used
Black | Ground         | Connect to circuit -
Shield|                | Not used (probably connects to laptop ground)
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  • \$\begingroup\$ I'll try that. Thanks. So the potential divider won't work? \$\endgroup\$ Feb 13 '16 at 12:41
  • \$\begingroup\$ Very good answer ! I did not consider a USB supply \$\endgroup\$
    – MaximGi
    Feb 13 '16 at 12:41
  • \$\begingroup\$ What do i do with the earth wires? \$\endgroup\$ Feb 13 '16 at 12:52
  • \$\begingroup\$ I presume you mean the shield / screen. See update. If you have a USB charger you may wish to use it in preference to your laptop. Cost of replacement will be less if you have an accident. If you're only running a few LEDs or similar from your PIC it is very unlikely that you could cause any damage. \$\endgroup\$
    – Transistor
    Feb 13 '16 at 13:06
  • \$\begingroup\$ @HasanImtiaz: The potential divider might work but consider what would happen if the PIC went from drawing almost zero current to drawing 20 mA. The voltage would collapse from 4.5 V to, maybe, 2 V. You need to regulate the supply. \$\endgroup\$
    – Transistor
    Feb 13 '16 at 13:23
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You could try to use a voltage divider along with a voltage-buffer OpAmp. (if you connect the pic directly the voltage diviser output, it will not work since it will draw current)

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  • \$\begingroup\$ I don't have access to many things, which is why i am asking otherwise i would order a 3x AA battery pack, but delivery is 10 pounds and I don't want to spend that kind of money for a 50p thing. Will the potential divider work? I'm asking because i have only just started my ecpirience with electronics? \$\endgroup\$ Feb 13 '16 at 12:38
  • \$\begingroup\$ voltage divider alone will not work, because its output current has to be zero, that's why I was suggesting a voltage buffer. Can't you just buy those 3 AA batteries in a shop or something ? \$\endgroup\$
    – MaximGi
    Feb 13 '16 at 12:40
  • \$\begingroup\$ Then how would i connect it to the circuit? \$\endgroup\$ Feb 13 '16 at 12:43
  • \$\begingroup\$ What about wires ? \$\endgroup\$
    – MaximGi
    Feb 13 '16 at 12:44
  • \$\begingroup\$ I understand how it would work with a 9v battery. How'd i do that with aa batteries \$\endgroup\$ Feb 13 '16 at 12:51
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Simple : Use voltage regulator L7805.(as @transistor already answered)

vr

Output voltage : 5.2V approx(always more than 5V if input voltage 9V or more)

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If cost permits, you may want to have Linear Technologies LTM4623 micro switching power supply module. This finger nail size chip can buck down 9v to 5v at 85% efficiency, just needed a voltage setting fixed resistor and two equally tiny capacitors at input and output. Great performance for battery powered loads. The only concern it costs usd10 a piece. Check their website.

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