Please comment on my data logger design

Projects General Guidance
1

I started out to build a data logging rain gauge, and that is still the plan, but I thought I might as well throw in a temp/pressure sensor to get more useful data. So I went looking for an Arduino data logger design but didn't find much (there are plenty of bits and pieces on modules but I plan to build a few of these and deploy them in the field so wanted a design on a board). Anyway I finally decided to try to design a more general purpose data logger on the basis that it might be useful to others.

I have built version 1 of this unit and works OK, the schematic below incorporates the lessons learned and is what I am planning to use in "production". Basically it's an ATMega328 with a Micro SD card and a DS1305 RTC. The DS1305 was chosen because it has Alarms, one of which is connected via a jumper to one of the interrupt pins - this allows the ATMega to be woken up from sleep on a schedule, to read temp/pressure every hour, say. The DS1305 has a backup battery so it retains the time when the main battery is being changed. I have provided connections to some digital pins, including the interrupts, analog including the TWI pins, Serial and a programming header. The SPI CS lines have pull-ups. There is a jumper to disconnect the voltage regulator so that the unit can be powered from the programmer or the reg. can be bypassed or whatever. There is an LED for general use.

So it is with some trepidation that I post this on here, but is there anything I have missed? Any other features that could be useful on a general purpose data logger? Constructive comments welcome...

Datalogger.png
Datalogger.png3185×2114 74.2 KB

2

IC1 is not specified; what voltage is Vcc?

3

Thanks for taking the time. IC1 is a XC6201P332PR 3.3V regulator.

I should have said the aim is for low power battery operation and I have gone with the internal 8Mhz oscillator

4

Looks good, the only possible shortfall is no USB to serial interface so programing via bootloader not possible, only via ICSP,
or is that by design to keep costs and complexity to a minimum?

5

You may want to add an electrolytic capacitor of ~47uf on each side of the voltage regulator and add 0.1 uf decoupling capacitors on the supply line near controller, rtc, SD on pcb to avoid noise as much as possible.

6

Thanks guys, I left out USB to keep the power consumption and complexity down, you can always use another Arduino board as a programmer.

The primary use for this is in battery powered applications so no supply noise is expected but I'll look at the decoupling, in terms of how it fits on to the PCB. One of the things I have in mind for production of these PCBs is that I want to etch them using the toner transfer method and solder by hand, so I am trying to keep the PCB as simple as possible.