Automobile power supply for standalone arduino ATMEGA Chip

Using Arduino Project Guidance
1

Hi guys i am slowly working towards having my own board built utilizing the ATMEGA 328P-PU Chip and need some help with my power supply. This is going in my truck and as of now i am using a 100uFcap to a LM7809 Vreg then a 10uF Cap to the LM7805 Vreg then a 1uF cap then on to the chip. Is there a better way of doing this? I would like it to be a small as possible to reduce the overall size of my PCB.

Thanks so much guys!

Mitch

2

Keep the power supply off the board - use a USB adapter that goes in a lighter socket.
http://www.amazon.com/s/ref=nb_sb_ss_c_0_8?url=search-alias%3Dautomotive&field-keywords=usb%20car%20charger&sprefix=usb+car+%2Caps%2C171

I picked one up at my local hardware store, and ran an uno for days on it just to make it run & check it out - no issues seen.

3

Thanks for the input! I guess i should have been a bit more clear and said that i want to hardwire it into my truck.

Thanks

Mitch

4
5

Why not just use a 7805? I don't see the point of the 7809. Especially since you are using a standalone chip and low power draw.

6

Auto voltage can be nasty - with like 40-50V spikes. Those can overwhelm a 7805.
See top of page 7 as an example of absolute limits:
http://www.st.com/web/en/resource/technical/document/datasheet/CD00000444.pdf
for these parts
http://www.dipmicro.com/store/L7805CV
http://www.dipmicro.com/store/L7805ACV

7

Would the capacitor before the voltage regulator not absorb most of these spikes? I think a basic lm7085 would get too hot dropping 14V down to 5V dont you think? I want to keep this as small as possible but reliable as well. The components must also be rated to operate in -40C temperature as this is going in my truck permanently and it gets pretty cold here in Canada. Would a switching voltage regulator be a better option? I have heard of them but never used one nor do i know much about them.

Thanks

Mitch

8

All the lighter type adapters are switching regulators.
You can get a fused lighter socket, hardware wire that in, then plug the USB adapter into it.

9

If my prototype goes as planned I might take this to production as i have a few people interested in it so i want this to be as proffesional as possible. I do like the simplicity of the lighter socket idea but i dont think it would be the right choice for this.

Thanks

Mitch

10

If you intend to distribute your product then a suitable automotive electrical noise and spike protection circuit is absolutely required. Polarity reversals (e.g. during jump starting) and spikes of hundreds of volts are occasionally encountered in automotive electronics. You can buy surge protection chips or build your own. I've attached a document describing the hazards as well as a DIY circuit that I've found useful (after frying some of my own electronics in a vehicle). In the circuit, that 1.5KE18 Zener diode is a 1500 watt spike suppressor, and costs about $0.25 at Mouser. Of course a fuse should precede it. The circuit also protects against polarity reversal and reduces radio frequency noise.

Tyco_AutoNetwork.pdf (49.4 KB)

Automotive_Filter.png