PIC DAS

PIC Based - Data Acquisition System

By: Steve Hageman

 

The PIC DAS Project: Inside and Out!

As seen in the January 2001 issue of QEX magazine.

For information on article reprints, click here.

 

How about putting a computer controlled, 12 Bit Data Acquisition System that you built on your own workbench! The Hagtronics PIC DAS project published in QEX is just that!

 

 

Why pay hundreds for a commercial Data Acquisition System when you can build the PIC DAS for less than $50.00? The PIC DAS is built around a Microchip PIC16C63A microcontroller and contains an 8 bit bidirectional Digital I/O port, 12 bit, 8 channel A/D converter and a 12 bit, 4 channel output D/A converter. It is perfect for quickly controlling any project on your workbench! Use the Digital I/O to sense switch closures with the help from the built-in weak pullups, control OPAMP's, power supplies and the like with the built-in D/A converters. Measure temperature or sense voltage or current with the built-in A/D converter. The real usefulness of this system is that it has a known simple to use interface that uses real ASCII commands over an RS232 link. This method of control saves programming time that would otherwise be wasted controlling the test setup, instead of actually doing the test.

 

Click here for a larger view

Here is a sample PIC DAS application using Agilent VEE to control the PIC DAS hardware.

The application read and plotted the inside and outside temperature for 24 hours.

The yellow trace is the inside temperature and the cyan trace is the outside temperature.

Here is a screen shot of a temperature measurement application using two LM35 semiconductor temperature sensors and the PIC DAS. The entire application was written with 16 statements in Agilent VEE (see below) to measure the temperature here at Steve's Workshop for 24 hours and then plot the results. Quick and easy, with excellent results, that's why I designed the PIC DAS in the first place.

As with all my projects, the firmware and programming examples are provided for free. If you need a preprogrammed PIC I can supply those also if needed (see below).

I hope you enjoy building and using the PIC DAS!

 


PIC DAS TYPICAL PERFORMANCE

Digital I/O ports....................................................... 1, 8 bit (With selectable weak pullups)

A/D Conversion

Channels..................................................... 8

Resolution................................................... 12 bits ( 1 mVolt / bit )

Input Range................................................. 0-4.095 Volts

D/A Conversion

Channels..................................................... 4

Resolution................................................... 12 bits ( 1 mVolt / bit )

Output Range.............................................. 0-4.095 volts

I/O Connections...................................................... Via 26, quick connect, screw terminals

Programming

Programs via 9600 Baud RS232 connection to a PC. Programming is via standard ASCII commands

May be programed in DOS or Windows. Includes a 32 bit Windows ActiveX control for super simple

programming with any 32 bit Windows development environment or may even be used with Excel to

directly input readings, etc into a spreadsheet.

Power Source............................................................ Internal 9 volt battery

Size............................................................................ 8 x 3 x 1"


PIC DAS Project FAQ's

Please e-mail with your questions. That's how this all works, you share with me, I'll post it so everyone knows -- and I'll give you credit too!

 

Article FAQ:

1) A simple, brief programming guide for the PIC DAS can be found here.

2) A reoccurring question is 'How fast is...", usually used in conjunction with the A/D converter. Well with 9600 Baud communication a character is sent every 1 millisecond (mSec). The A/D command requires 5 characters minimum to start a conversion going. That's 5 mSec. The PIC DAS takes only hundreds of microseconds to make the conversion, then the results are sent back to the PC. The data sent back is 2 to 5 characters long depending on the A/D voltage (i.e. the A/D code is 0 to 4096, plus a carriage return), so this time is 2 to 5 mSec long. Hence the total conversion time is somewhere in the range of 10 Milliseconds minimum. The host language adds time depending on what happens to the data when it returns. As a test, 1000 A/D samples were made with a simple QBASIC program on a Pentium 200 CPU, the data was returned and simply discarded (it was not printed or plotted as this takes a huge amount of time). The elapsed time was 12 mSec per sample, or 12 seconds for 1000 samples. The DAC can be calculated in a similar manor, but suffice to say that a typical update time was also approximately 12 mSec per update point.

 

Parts / Hardware FAQ:

I will be keeping folks abreast of where to get parts, etc. for the project here:

1) The complete parts lists for all the project is available here as a text file.

2) A PCB is available for the project from FAR Circuits. Check with FAR directly please, as they supply the PCB's, not me.

3) An assembly drawing for the FAR Circuits PCB is available for download here (GIF Format).

4) A schematic of the PIC DAS is available for download here (GIF Format).

5) A preprogrammed 16C63A PIC is available from me for $20 US Dollars. Shipping to the 'ol US of A (and Canada, Eh?) is FREE. Shipping to Europe is $5.00 (Via US Post Office Global Priority Mail). Shipping to South America is $10 US Dollars (Via anyway I think it will get there!). Sorry South America, the postal system down there just looses too much of what I send.

6) The Maxim and Microchip PIC parts are usually available as samples. Check this out at www.maxim-ic.com and www.microchip.com. If you can't convince them that you deserve samples, then Digi-Key will gladly sell you the parts.

7) C9 is shown on the schematic but does not exist on the layout, just omit C9 when building the PIC DAS.

 

Software / Firmware FAQ's:

1) The associated application software is available free as PIC_DAS.ZIP at the ARRL/QEX files site. The PIC DAS may be run from DOS or Windows 95, 98 and NT (Also hopefully Win2k, but not tested yet).

2) A sample QBasic program that exercises all of the functionality of the PIC DAS is available for download here. This should be useful if you wish to program the PIC DAS from a standard BASIC or from DOS using QBasic. Depending on the computer OS and speed you may have to fiddle with the delays some.

3) For Windows 9x, NT and above, I have created an ActiveX control that automates the programming process greatly. The ActiveX control may be used with Visual basic, Visual C++, Delphi, Agilent VEE and even Microsoft applications such as Excel and Word. To download the ActiveX install file click here to download picdas_activex.zip (1.7 meg file).

4) Only use Winzip or some other 32 bit (i.e. long file name aware) unzipping program, otherwise all the long filenames will be truncated to the old DOS 8.3 format and the program will refuse to install !!!

5) Overwriting of outdated files during install the should be safe as these files are all genuine, Microsoft files. If you don't feel safe about this, note the name of the file name(s) the install program want's to update, respond NO to the prompt(s). Then find these file(s), copy them to a floppy and reinstall the program. This way if anything goes wrong, you can recover from the problem.

6) You can uninstall the ActiveX control program by going to -> Control Panel -> Add/Remove programs.

7) I write all my firmware for the PIC's with the CCS PCM C compiler (Hey, life is just way too short for all that assembler stuff ;). This is really a fine little compiler, and the best $99 dollar compiler since QuickC ! Heartily recommended (the Hagtronics 'Two Thumbs Up'). The PIC firmware source code can be downloaded by clicking here. If you can program a PIC16C63A yourself , the firmware download contains a HEX programming file. This HEX file contains the fuse settings and works with a Microchip PicStart Plus programmer. Sorry I can't support other programmers, please contact your programmer manufacturer and ask them how to load a genuine Microchip HEX file!

 8) Copyright: The software/firmware is freeware when used with the PIC DAS project as described in QEX. If you want to use the software for any commercial purpose, then all I ask is that you contact me for a license. Fair enough?

 

PIC DAS Applications:

Computer controlled power supply test system


References:

Agilent Technologies VEE - Test Programming made fun!

[1] For more information on Agilent VEE, a graphical test programming language, check out the Agilent Technologies web site at, www.agilent.com/find/vee.

[2] For more information on using ActiveX controls with Excel, check out Werner Haussmann's articles in Test And Measurement World. Search the article archive for 'Haussmann' or 'ActiveX'.

 


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Updated - 26Aug07

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