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Topic: Car Keypad (Read 43938 times) previous topic - next topic


My board came in today and it looks good!  I can't wait to get home and try it out.  I ordered two, just in case I royally mess the first one up on assembly. :)  I really would hate to have to wait a whole extra month.  I'll post more pics when I get it all put together.




So here I am, closer to the inevitable car door cutting.

Populating the board:

I got a little better as I worked from right to left. I didn't realize how little solder that SMD parts required.

All assembled:


Testing the board:

Everything works perfectly!

Fitting into the box:

The screw holes line up perfectly. The connectors on each end were a bit taller than I had expected, though. The lid still closes, but it pinches the wires a bit. I'll trim a little useless plastic off the top of the connectors and it should be fine.


May 11, 2009, 07:40 pm Last Edit: May 11, 2009, 07:47 pm by george_graves Reason: 1
VERY COOL - I love to see an arduino put to use in the "real world"

I didn't see much power protection going on there.  What are you doing to keep away nasty voltage spikes and reverse voltage?

(a car's power is notoriously bad)


Thanks George!

I'm not exactly an EE, so I'm real green on most of this.  I knew that car voltages can be nasty, but as per other discussions around these forums, people have been running Arduinos from cars seemingly fine.  The datasheet for the Nano says it should be ok up to 20v.  I hadn't even considered reverse voltages at all, does this tend to happen on a car?  For reverse voltage, one would throw in a diode on the power line?  As for the spikes, a capacitor on the power line?

Honestly the only thing I considered was a drop in voltage on cranking the car.  I doubt much that anyone is going to be using the keypad while cranking, so I didn't think a restart would hurt anything.  I suppose that the dip could lock up the chip instead of just restarting it.  I'll be actually running it in my door soon, so I'll have to see.

If you have any good suggestions for cleaning up the power, or maybe a good place to look, let me know.


May 12, 2009, 05:59 pm Last Edit: May 12, 2009, 05:59 pm by designer2k2 Reason: 1
great project  :)

you should consider some safety for the arduino, there is quite some noise there!

i made this:

just take the input part, that should block the biggest problems



So the 1N diode keeps the current from flowing backwards, the zener diode would cut out voltages above 15v, and the choke would clean up the power a bit.  What exactly do the two different caps do?  Decoupling to clean up the power?  Something else?

I assume that everything to the right of C3 I should ignore, as I don't want to reduce the voltage to 5v?


Yes, you dont need C3,IC1,C2 when it should only protect  ;)

L1 blocks HF noise (should be 2A cappable).

the 1N makes in case somebody messed up the polarity a safety, and in case the input drops it prevents the C1 from getting discharged.

D2, can also be a 20V type, this limits the voltage.

C1 (Ultra Low ESR) smoothens out small ripple.

C3 could be removed, but im used to always put C3 and C2 with a 7805  :)


Maybe I'll work this into my board when I get home.  This would mean waiting another MONTH before I could install, though.  Ugh.


Nice and clean prototype work,  First class job.
Keep on building,
make stuff.




where did you make your own pc board =D

id like to make my own ;D


I used http://BatchPCB.com, which is a service of SparkFun.  It's relatively cheap, but it takes a month or so to get your board.

You'll need to learn Eagle (or similar).  There's a tutorial on PCB layout using Eagle on SparkFun's site here:


wow >_>

well, i can wait a mont to get started on arduino sheild making lol


May 14, 2009, 04:54 am Last Edit: May 14, 2009, 05:44 am by neonpolaris Reason: 1
Would this work for L1?

And for C1, can I use a ceramic here, or only electrolytic?  I'm thinking of longevity and temperature sensitivity, but I'm not terribly sure of when I can use one.  If ceramics are non-polar, can they always replace the others, but not the other way around (like when dealing with AC)?


Ok, here's the cart I'm looking at, ignore the amounts:

I may not have room for that choke on the board!


yes, that L1 looks good!

for C1 it should be a ultra low ESR electrolytic. Thats becouse they are like the "fastest" and you can get them with big F values.
elextrolytic is fine, as long as you dont take the super cheap ones.
my C1: http://shop.conrad.at/ce/de/product/445903/KONDENSATORULTRA-LOW-ESR220F35V
its rated with 6000h at 105°C, that should be enough...

in your chart you have a 220pF, what should be a 220µF  ;)
and with a 20V zener diode your still safe but it will not be so close to trigger unwanted (14,4V is quite common in a car)

thats how this looks in my prototype:

(my 1N is a little oversized, had no smaller around ::))

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