BASIC Stamp, Microchip PIC, 8051, and Remote Control Projects

Interfacing the BASIC Stamp I Rev D to the


Velleman K2645 Geiger-Muller Counter
By: Ernie Negus

Project Designer: Ernie Negus
Project Files: gieger.zip
File Size: 232K
Email the designer at: nernie@uswest.net
Visit Ernies' Web Site at: http://www.users.uswest.net/~nernie

This project interfaces a Basic Stamp I Rev D with the Velleman K2645 Geiger/Muller counter kit and a Hitachi compatible one-line LCD panel display. More info on the Velleman kit is available at the following URL: http://www.velleman.be

The zip file available HERE, contains schematics for the interface and programs that:

  1. Allow you to use the stamp to convert the beep counts to a standard unit
    of measuring gamma and beta radiation.
  2. Display this on a one-line LCD panel display (Radio Shack Catalog
    Number 910-4913).
  3. Log this measurement hourly or every four hours to the stamp's internal
    EEPROM memory.
  4. Interfaces the Geiger counter to a PC for graphing and analyzing data in
    real-time or from logged data.

The project is low power and can run on one 9 volt battery continuously for up to two months. It can log low to unhealthy radioactive levels (under 256 microrems) to the stamps internal EEPROM memory for up to one month, or very high radioactive levels for up to two weeks (sampling rate: every four hours).

It can be used to determine the radioactivity caused by computer monitors, television sets, microwave oven leakage, gas furnaces, etc. It can even be used as a lightning detector during thunderstorms. It has a resolution of 6.67 microrems/hr and has a range of 0 to about 3433 microrems/hr.

Radiation Levels:

  1. Low radiation is below 10 urems/hr.
  2. Normal background radiation is in the range of 10 to 79 urems/hr.
  3. High background radiation is in the range of 80 to 129 urems/hr.
  4. Unhealthy background radiation is in the range of 130 to 149 urems/hr.
  5. Safe only in short term exposure levels are 150 urems/hr to 249 urems/hr.
  6. Dangerous radiation levels are above 250 urems/hr.

Additional Requirements:

  1. Velleman Geiger/Muller Counter Project kit # K2645 available at many electronics stores, or from the website above. Cost is $120-$140.
  2. One CMOS CD4040 12 Stage Ripple Counter. About 69 cents from Jameco Electronics.
  3. One CMOS 74C157 Quad two bit data selector. About $1.49 from most Radio Shack stores.
  4. Five 10K 5% 1/4 watt resistors.
  5. Two 100K 5% 1/4 watt resistors.

Optional:

  1. Radio Shack (RSU#: 11453461) or Hitachi compatible one-line LCD display for display of radioactive levels.
  2. Dual row IDC Female connector (w/through-hole solder lugs) for connecting to the LCD display.
  3. A 100K trimmer potentiometer for adjustable LCD display contrast.
  4. 9-pin D-Sub female connector and straight-through cable for interfacing to a PC.
  5. Plastic case 5.75 x 3.60 x 1.29 inches with 9V battery compartment (Radio Shack Cat # 270-213).

Design notes:
Mount the LCD display as far away from the Geiger tube as possible. The 600 Volts on the tube may cause the LCD display to flicker or display random characters.


LCD Display In Action

I added a sliding power switch to interrupt 9V to the Stamp circuit and Geiger counter. I also brought out a six pin single inline header for the three pin parallel port programming interface and the two-pin serial interface. Pin four was removed to serve as a separation key. I used a 9 pin sub-D female connector and soldered a two-pin connector to pins 5 (gnd) and 2 (tx). This connector plugs into the serial port of a PC via a straight-through serial port extension cable.

Click HERE to view the project schematics in your browser.

Operation:

The CD4040 is used to count the Geiger ticks. The clock input is connected to the middle of two series 100K resistors. One of the resistors is connected to ground and the other is connected to pin four of IC U1 (the CD40106 or 74C14) on the Geiger counter.

The Stamp may be powered from the same 9V battery as the Geiger counter. The 74C157 data selector allows the stamp to read 8 bits of the counter, one nibble at a time. The 9th bit is read by the stamp while the LCD display is tri-stated. All other bits are discarded, allowing up to 512 counts in a one minute period or 3433 microrems/hr maximum.  The A/B selector on the 74C157 doubles as a serial output for the PC interface. 

The program puts the stamp in sleep mode for over 90% of the time to conserve battery power and provide crude timing. The Geiger counter reading is updated once per minute and is based on the total counts received -- from between one minute, and four hours of operation. The longer the device is operated, the more accurate the readings will be. The formula for converting counts to microrems/hr was derived from the response table included with the Geiger counter kit. This formula is:

microrems/hr = counts per minute * 100 / 15

The BASIC Stamp I program GEIGER3.BAS calculates this every minute, and also averages this out so that it uses:

Total counts since run started / Total minutes running * 100 / 15

The average value is displayed for ten seconds after the by-the-minute value is displayed.  As-is, the program does not reset the accumulators, so the accuracy of the averaged values is only good for four hours and fifteen minutes after the unit is turned on. The maximum value is also stored and displayed after the average value. The Stamp sends the minute-by-minute reading out as numeric data, followed by a carriage return and line feed at 2400 Baud.

The Stamp I programs, GEIGER1.BAS and GEIGER2.BAS don't use the LCD display.  You should disconnect the LCD when using these two code files to conserve battery power. GEIGER1.BAS will log up to 13 days worth of 16 bit measurements to the Stamps internal EEPROM. GEIGER2.BAS will log up to 26 days worth of 8 bit measurements to the stamps internal EEPROM. Both programs log the average urems/hr data after one or four hour periods.

When the Stamp is turned on, this data is immediately sent out through the serial port at 2400 Baud.  The data is sent numerically with a line feed and carriage return after each number, the earliest measurement first. The Stamp will start collecting new information, starting from zero, if it is left on for more than a minute after dumping the data. Old data is overwritten and not cleared, so if you want to start with cleared data, you should reprogram the stamp before each use.

Here are photos of the project enclosure you can view directly in your browser.

  1. Click HERE to view the BASIC Stamp connected to the Velleman K2645 Geiger/Muller.

  2. Click HERE to view the project with serial cable.

  3. Click HERE to view the project schematics.

Thanks for sharing your project with everyone Ernie.  Great job....;o]
 

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