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I have had some difficulties finding a barebones Arduino board and have had the following made. I just wanted to see if anyone could spot any issues? I think it has everything. I'm really trying to get it as minimalistic as possible, but at the same time able to use a power source like a 12v/24 battery. Any help would be greatly appreciated. Many thanks

https://i.stack.imgur.com/zlwQT.png

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  1. You shouldn't put a capacitor under the chip like that. In fact I don't much like the layout of the whole crystal circuit at all.
  2. You need capacitors on the 7805 regulator - around 10µF on both the input and output.
  3. The RESET pin needs a pullup resistor otherwise the chip won't function at all.
  4. You need decoupling capacitors on all VCC pins on your main chip.
  5. Instead of meandering ground traces you should use a ground pour.
  6. Running from the kind of voltages you propose the 7805 is going to melt. You will need a BigAss™ heat-sink on it. For those kind of voltages you would be better using a switching (aka buck) regulator. Maybe as an off-board module to keep your board simple.
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  • Many thanks for your help Majenko. Do you think there is any way to get around the issues with the board as it is? I've (foolishly) already sent 10 of those to print. I'm guessing with 1, I could add the capacitors off board. Also doesn't the 1N4007 help at all? – oduffy Jan 5 '17 at 19:45
  • Most things you can work out a way to solder them in afterwards. The biggest issue will be heat from the regulator. By adding a switching regulator on a separate board to feed the 7805 you would solve that problem. Regulate down to about 7v. – Majenko Jan 5 '17 at 19:48
  • The 1N4007 will just drop 0.7V so does very little in the scheme of things. It is really only for reverse power protection. – Majenko Jan 5 '17 at 19:49
  • Ah I see, so putting something like this to feed the 7805 should solve the problem? ebay.eu/2hVTZRX – oduffy Jan 5 '17 at 20:19
  • No, exactly oposite of that - step-up converts low voltage to higher (say input 3.2V and output of 7V (to feed your own 7805). You want step-down (like this one ebay.co.uk/itm/… or any other with Input rang covering yours 12-24V (rather little more) and OUTPUT of 7V for your 7805. Maybe you can even go with some outputting 5V and big capacitor to filter the switching noise, if you want risk and save more money. – gilhad Jan 5 '17 at 20:42
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C4 is under the IC, which may (or may not) do problems, regardless which side of PCB you place it actually. The reset is better to connect via resistor to defined level than to leave floating. Usually there is also capacitor there to delay start until power is stabilized. I would put big capacitor near the stabiliser (also I think, it is recomended by manufacturer of the stabiliser for a reason), but maybe if you have good batery and short wires, it could work too. Also small capacitors between GND and VCC as near the IC as possible are common to reduce noise. And reset button is usefull add-on, but not necessary. Anyway I think, it could work as it is (with the reset defined).

If you have some particular application in mind, then you may use also different layout and/or get more connectors for some pins (some of my "arduinos" does not look like Arduino at all, having all periferials on the same PCB instead on some shields.

also http://download.gilhad.cz/arduinobb_12.jpg this is fully working arduino, which I used many times - so you do not miss anything critical (those LEDS are not necessary)

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  • Many thanks for your help Gilhad. With regards to the reset, would connecting it through a resistor to ground solve the problem? Majenko (above) said it probably would not work without this. – oduffy Jan 5 '17 at 19:52
  • No, that is a boost regulator. You want a buck regulator (step-down). They do some that look very similar to that one. – Majenko Jan 5 '17 at 20:32
  • Yes, he was right (in some way) - depending of intended use the resistor can be onboard, or offboard or managed some other way (as output of some othe system, or programmed to be NOT reset, but I/O, for example). But fof simple generic Arduino board you should put there resistor and if you already send it to production, then just solder the resistor over the board - ugly but sure work. – gilhad Jan 5 '17 at 20:37
  • With regards to the reset, would connecting it through a resistor to ground solve the problem? - no, /RESET needs a pull-up resistor. Something like 10k soldered from Reset to Vcc. – Nick Gammon Aug 3 '17 at 4:49

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