Simple data logger

[helicooper]

Hello all,
Let me preface with this with the fact that I am very very new to all electrical engineering and programming. My first and most important question has to do with cost.

I am looking into building a data logger that will be able to log voltages. This data logger needs to be able to take 4 channels of voltages and log them with a very low tolerance of error (sub millivolt-millivolt. Channel 1 needs to be logged every 5 minutes while channels 2-4 only need to be logged every 6 hours. The data logger needs to have onboard memory (enough to log the data for up to 3 months or possibly only 1 month if this becomes a cost issue), onboard power (for now only enough power to run for a couple days), and a way to start and stop the logging preferrably with an led light indicator of when it is recording. The logger also needs a usb plug that can act as a way to transfer the data to the computer. The board once finalized would only need to be programmed once. I apologize if this is too vague or not articulated enough/correctly.

EDIT: 2nd and 3rd questions answered on sticky post I should have read first. Thanks!

Thank you all for your time for a complete rookie.

 

[StudentSA]

Since you would like to use USB as a communication to your PC I think a PIC18F4550 would be a good start.

This microprocessor is designed to handle USB communications with a PC and can easily be interfaced with external memory (EEPROM).
The PIC18F4550 also has alot of I/O pins that can be configured to record the voltage levels up to 12bit resolution.

It can also be programmed to use power saving modes that would allow it to run off a simple 9V battery for quite some time.

Do some research into this IC.

 

[Wp100]

Hi,

You have many options to choose from - first the chip, the 18F4550 is a common choice for usb connectivity, if that is a requirement, but also look at other chips like the 3.3v pic24 usb versions.

You really need to have some idea of how many bytes of info you need to store each time so you can actually work out the total space needed for your time period and also into methods of condensing your info the minimise the space needed

EEprom , either onboard the pic chip or external chips may handle the volume and is quite easy to program up.

For larger volumes then an SD card would be the answer, this would have the advantage of being removable as well as being able to usb transmit the data to a laptop.
The downside its the programming is a lot more complex.
See Microchips site for the many pages of free info and code for both the USB and SD card.

A led is a good status indicator, but consder a lcd display, this will give you much better visual control of the comms and also allow you to interrogate the current and stored readings in situ.

As for your ' only need to program the pic once' - don't believe yourself !
You will always find ways to improve your program, so when you design your ciruit make sure you include ICSP - its only a small connector and a cople of cheap components - well worthwhile.

 

[Mike - K8LH]

Dear helicooper,

Can you tell us the range of voltages you need to measure? That would help qualify the use of devices with more or less 'standard' 10-bit ADC modules for the voltage measurement.

Instead of using a relatively large and expensive USB enabled device for relatively infrequent data 'dumps' you might consider using a smaller and less expensive device and a usb-to-serial adapter cable. I use a modified $3 Chinese clone Nokia CA-42 cable for USB communications with even the lowliest 6-pin 10F200 device.

Cheerful regards, Mike

 

[helicooper]

Dear helicooper,

Can you tell us the range of voltages you need to measure? That would help qualify the use of devices with more or less 'standard' 10-bit ADC modules for the voltage measurement.

Instead of using a relatively large and expensive USB enabled device for relatively infrequent data 'dumps' you might consider using a smaller and less expensive device and a usb-to-serial adapter cable. I use a modified $3 Chinese clone Nokia CA-42 cable for USB communications with even the lowliest 6-pin 10F200 device.


Cheerful regards, Mike

Thank you all for your responses and time. The range of voltages will be very small from 0VDC-3VDC. The idea for this board is to be able to eventually produce it in quantity for as little as possible while also making it simple for any housewife to be able to plug it into the computer and have the data displayed. If I can't produce the board for under 25 dollars then I just need to scrap the idea.

 

[Pommie]

The 18F13K50 is a full speed USB 2.0 enabled device that is less than $2 in low volume and $1.40 in larger volumes. So the final cost really depends on the rest of the circuit.

Mike.

 

[helicooper]

Great info. Thank you.

 

[kjennejohn]

I recommend you use the Nano processor. This is a PIC bootloading processor with a powerful BASIC, freely available for a simple download and installation. This is from BasicMicro(.com). They have been around several years.

To develop your design, you need to buy the $8 Nano18 IC, an 18-pin, 5V, DIP format part. This has everything you need built in, except for the USB. It has an 8 MHz internal clock, so you save the expense and trouble of a crystal or resonator. It has five ADC pins, internal RAM and EEPROM. It will run on 4V to 5.5V, so battery operation is OK. Their data sheet says 4.9 to 5.2, but the manufacturer says 4 to 5.5, so just go with it.

For development, you can purchase their $20 Nano Prototype Board, the data sheet being here:
https://www.electro-tech-online.com...o_microcontroller_prototyping_board_B0110.pdf
This can be powered off an AC adapter or battery pack. To program on this, you need their $15 Nano USB programmer/serial cable:
**broken link removed**
That's $43 so far, not counting shipping/handling.

When you're done developing and want to lay the board with USB capability, you can use the schematic from this development board to see how to use the FTDI USB-Serial IC to provide USB comms to a PC: https://www.electro-tech-online.com/custompdfs/2010/06/basic_atom_nano_development_board_B0082.pdf
You need to supply software to do the serial comms, but that can be done in VB or something.
Good luck with your project.