PCB considerations with microcontrollers?

justDIY

Active Member

• Dec 18, 2006

• #21

HarveyH42 said:

Figure sinse they are flashing, not constantly on, everything could handle a little abuse, and I'd get brighter output.

Click to expand...

lots of projects drive leds directly from the pins, relying on the internal resistance of the switch(es) to limit current. it may not be a wise choice for a commercial product designed to sell in huge quantities, but for a homebrew project, it is something you may want to consider.

 

H

HarveyH42

Banned

• Dec 18, 2006

• #22

Success!!! The 4.7 uf cap across the IR module's power leads did the trick. Also had to point the IR module and IR LED away from each other slightly. And as a bonus, detects my hand at a little over 12 inches.

 

H

HarveyH42

Banned

• Dec 18, 2006

• #23

Attached is a better schematic of what I have on the working PCB. Let me know if you see anything I need to fix before doing a new PCB from it.

 

Attachments

• Tiny13Police.jpg

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justDIY

Active Member

• Dec 18, 2006

• #24

if I had to choose, I'd move C2 to the output side of the 78l05, as the input capacitor is optional, the output capacitor is not (according to the datasheet).

does the ir gizmo really need 4.7uf to decouple it?

how about a 0.1 uF cap for the cpu, just to make all us worry-warts happy

 

H

HarveyH42

Banned

• Dec 18, 2006

• #25

Made the changes. Probably have to go with thinner traces to keep the board small...

One of the post suggested 4.7-47 uf on the IR module, tried it, fixed the problem. Maybe this was why I couldn't get it to work with pin change interupts...

 

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• Tiny13Police2.jpg

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mramos1

Active Member

• Dec 18, 2006

• #26

Last schematic is perfect. I was gonna say, you to not need the input CAP as using a battery.. But JustDIY got that. And it was too small for real use anyway there.

And moving it where you did, you have the decoupling you need since you have a 38Khz signal on it.

But I think it will work without that cap all together

 

K

kchriste

New Member

Forum Supporter

• Dec 18, 2006

• #27

I was gonna say, you to not need the input CAP as using a battery.. But JustDIY got that. And it was too small for real use anyway there.

Click to expand...

He could also just put the pads on the PCB and not install it.
Maybe a diode in series with the B+ line from the battery in case someone accidentally brushes the contacts across a battery the wrong way.

 

justDIY

Active Member

• Dec 18, 2006

• #28

the vreg's internal reverse polarity protection should protect from a 'brush', but an external diode would be cheap insurance

edit: just to add ... personally, I loath the 9v battery. they are expensive and impotent. how about running your kit off two, three or four AA size batteries, then you can do away with the regulator... since right now, your vreg is burning almost as much power as it is regulating (9v - 5v = 4v to burn), things get better as the voltage drops

 

Last edited: Dec 18, 2006

mramos1

Active Member

• Dec 18, 2006

• #29

justDIY:

That is how I do it.. 2 or 3 AA or AAA cells are great. No drop/lose.

EDIT: Taught years ago. If battery, no regulator.. I cannot name the one that yelled at me. You all know who you are!

 

Last edited: Dec 18, 2006