Arduino+Breadboard to custom PCB project

I have been working on an Arduino based project for a while now and it's getting the point I'd like to make it more permanent/professional looking by building a custom PCB for it. I'm not looking to make a shield, but rather I'd like to convert my project to a standalone board. I know the next step is to breadboard everything out (no more arduino boards, but use a ATmega328 with Arduino Bootloader).

The project currently consists of two Uno's talking over a simple 315Mhz RF link. One side collects temperature readings via some thermistors and the other has an LCD display, SD card & DS1307 for data logging. I need to add some buttons for navigation and a buzzer/alarm on the receiver as well.

I'm learning Eagle and have even started creating custom parts that I'll need, but I could use some advice:

  1. The thermistors, DS1307 & RF links run at 5V while the SD/LCD are 3.3V. I'm trying to figure out the most cost effective/simplest way to generate both voltages off a pair of AA batteries.

I know I can use an NCP1400 to step up to 5V... should I split that output to a 3.3V regulator? Seems like I'd be wasting a fair bit of power stepping up, only to step back down.

Perhaps the best way is just use 4xAA's and independent 3.3V & 5V regulators? Prolly would work as long as I don't use rechargeable batteries right?

  1. How can I calculate the power draw of a thermistor? Yeah, I'd read the spec sheet, but there isn't one.

  2. Any suggestions for references for de-Arduino'ing a project? I know I'll need to build a regulated power circuit and provide a crystal for timing. Makes sense to add a FTDI programming header too. Any other gotchas or things to think about?


Put your atmega on a socket, or socket strip, then plug it back into your Uno for programming. This place also has 16MHz crystal, 22pF caps, 100nFcaps, 10K pullup resistor for the reset pin. All the pieces on the lower left are the 'arduino' bits on a little board I made up. I have a 5V walwart for power, so no regulator is included, just a 100uF cap on the 2 pins where power comes in.

Thanks for the tip. I was aware I could always swap Atmega chips, but frankly that seems like more work then it's worth each time I want to update the code- shouldn't be that often, but I guess I'm at the point in this project that if it's worth doing, then it's worth over doing! I'm actually hoping to design my own PCB's (one for the receiver & transmitter) and either etch it myself or have them done via something like BatchPCB. That's a little bit farther down the road I guess though... I still need to figure out a good way to power both ends since I don't want to use a wall wart.

If you don't want to swap, then put in a 6-pin header like the promini uses to connect something like an FTDI-Basic to, and be sure to keep Rx/Tx free, or add a switch to disconnect the lines, so you can program freely. best price around, mine has been used many, many times since August.

Anyone with suggestions on cost effective ways to power a project like this? One idea I had was using a MAX756 setup like MintyBoost to generate 5V off 2-3AA's and then a 5V->3.3V step down regulator like the LM3901 for the SD/LCD, but I'm looking at over $10 in parts which seems a bit much (and that's not even using tentalum caps).

Sparkfun has a $6 NCP1400 5V step up breakout board which would shave off a about $3, but I'm a bit hesitant to use a breakout board for limited gain (I'm hoping to open source the project hardware & software so other people can build it and you never know when Sparkfun will discontinue a part). Trying to solder such a small SMD part like the NCP1400 seems way over my abilities (or the average hobbyist).

Still trying to figure out how to determine the power draw of a thermistor so I can run some calculations on my power requirements. I suppose I could just "wing it", but I figured that it wouldn't be too hard to do it right.