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Topic: My first pcb (Read 5 times) previous topic - next topic

harleydk

Hello,

I've managed to design my very first pcb. It's a sensor board, with room for an atmega328 and 3 analog inputs, as well as a status LED and a 2x4 pin-header where is meant to go a nordic transceiver breakout module.

I was hoping some of you more experienced fellas would help me out and take a quick look at it, and point it out if you immediately spot any obvious mistakes. I've doubled-checked connections and it looks ok in a gerber-viewer as well.



The power goes in and runs to a 5v voltage regulator, and I put a capacitor to smooth ripples. Also there's a resistor to avoid resets. The 2x4 pin header is placed as it is because the transceiver breakout module will 'overlap' the board, so I put it to one side. The voltage regulator will thus be 'sandwiched' between board and transceiver hanging above it - a potential heat problem? I'd like to power the board with a 9v battery.

Appreciate your input - thanks a lot in advance.

/Morten
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My hopefully helpful blog at technicalstuffhopefullyuseful.blogspot.com

Chagrin

You need to post the schematic.

I'm not familiar with the program you're using here, but if possible you want to fill the board with a ground plane to take heat away from the regulator. At worst you can do it manually by just adding a lot of extra, thick traces. Also, that regulator needs capacitors (typically electrolytic) on its power in and power out lines; if you don't include them your power will be fruity. You can always leave the spaces unpopulated if you find that you don't require them -- but can't add a capacitor if you find out you need them and don't have a space available!

Jack Christensen

Most regulators should have caps on input and output, refer to the datasheet for specific recommendations. On the ATmega, pin 7 (Vcc) should connect to pin 20 (AVcc). The ATmega also needs at least one bypass cap (100nF) near one of the power pins, and another from AREF to ground.

A schematic would be helpful, though.
MCP79411/12 RTC ... "One Million Ohms" ATtiny kit ... available at http://www.tindie.com/stores/JChristensen/

harleydk

Hello Chagrin,

very helpful indeed,


You need to post the schematic.


I'm posting a schematic here. The program I'm using - Fritzing - leaves a little bit to be desired in schematic view, in as much as one cannot decide the wire-colors and thickness in the schematic view (they appear as solid blacks when they're routed, but I like to leave the routing for the pcb view - the schematic-view will chance to reflect the routing I create there)




I'm not familiar with the program you're using here, but if possible you want to fill the board with a ground plane to take heat away from the regulator. At worst you can do it manually by just adding a lot of extra, thick traces. Also, that regulator needs capacitors (typically electrolytic) on its power in and power out lines; if you don't include them your power will be fruity. You can always leave the spaces unpopulated if you find that you don't require them -- but can't add a capacitor if you find out you need them and don't have a space available!


I'd rather go safer than sorry and will certainly on your say add the capacitors and the board fill (the Fritzing software has an option for this, so very thankful for your pointing it out, had not thought of that).
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My hopefully helpful blog at technicalstuffhopefullyuseful.blogspot.com

harleydk

Hello Jack,

thanks a bunch,


Most regulators should have caps on input and output, refer to the datasheet for specific recommendations. On the ATmega, pin 7 (Vcc) should connect to pin 20 (AVcc).


sorry if this is a stupid newbie question, in which case I can only hope it'll help some other hapless soul, when you say Vcc and AVcc should connect, is that then saying that these pins require a direct connection even though they're fed the same 5v from the regulator? Thanks in advance for clarifying this for me.


The ATmega also needs at least one bypass cap (100nF) near one of the power pins, and another from AREF to ground.


In terms of decoupling (bypass) capacitors, would it in your opinion be safe to say that 100nF is a safe 'norm' in dealing with  low-voltage projects such as this one? I'm asking because I've come across a number of tutorials on similar projects with somewhat varying values, despite the same amount of power.

Appreciate your input, thanks again.
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My hopefully helpful blog at technicalstuffhopefullyuseful.blogspot.com

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