OK, I really didn’t plan to put this on a robot, but it would be easy to do…
This is a Geiger counter that I just built, mounted in the case of a cheap transistor radio. The oblong thing along the bottom is a Geiger-Mueller tube, which is a detector for “ionizing radiation”, such as Beta and Gamma rays.
The small SMT board is one of my ‘stackable’ boards that I made a couple of months ago. It has a PIC18F2620 on it (way overkill for this project).
Just below the battery and to the left of the switch is an LED that blinks each time a particle is detected.
The large board is primarily a circuit for generating very high voltages (over 700 volts) at very low currents, necessary for the Geiger tube.
The PIC drives the voltage-booster using PPM (pulse-position modulation, similar to PWM). A small version of the output voltage goes back to a PIC A/D input, so it can actively regulate the output voltage (just like a switching power supply). A pulse from the G-M tube triggers an interrupt on the PIC, and it then blinks the LED. Note that the PIC could easily be used to measure “counts per minute” and such.
When operating, I get one count every few seconds, due to background radiation and cosmic rays and such. I also have an old wristwatch with a radium dial that outputs many counts per second when I hold it less than an inch or so from the tube.
So, for folks with a robot that has a ‘sensor for everything’, you probably need to add one of these to your bot…
A buddy of mine actually has a nuclear-decay-based random number generator that he uses for producing truly random number seeds. He took a geiger counter kit that provided a “total counts” figure via a serial output, and married that with a serial-to-USB converter. He epoxied a low-level source to the case near the G-M tube, and wrapped the whole mess in a sheath of lead sheeting. He uses the ‘total counts’ counter to provide true random numbers for (among other things) the ‘random play’ mode on his in-car computer’s MP3 player.
You continue to amaze me with your ability to whip up circuits. I do have one comment / question though regarding your designs:
Why don’t you use the 45deg. angles with traces? I often see a lot of traces that have variable angles as if it was drawn by freehand. Use the snap to grid and adjust the grid spacing as needed so the traces are consistent.
You can use a coarse grid for component placement, a medium grid for trace routing, and when needed, a fine grid .001 for attaching the end of the trace to the component lead. In some cases, you need to figure out the pitch of the component to match the grid to the pitch.
Thanks Mike. I guess I’m just not very concerned with how it looks, as long as it is functional and reasonably efficient.
Doing a layout in a cramped space takes a lot of time just to get something workable - some things are difficult to fit using snap-to.
However, I do use snap-to in some places, such as connector positioning (but on the board shown above, I messed up a bit - some of the 10-pin headers are 0.1" from each other, while a couple are 0.05"…).
Here’s a link to the schematic: www.geocities.com/saipan59/geiger/geiger7616_sch.jpg
The PIC “stackable” board is not shown, but there’s nothing interesting there - it’s just 2 outputs and 2 inputs from the PIC.
The SW in the PIC is currently very simple:
Main Loop:
Do an A/D reading on AN8.
If the voltage is below a certain value, then output a pulse on RB4 (the pulse is always the same width, a dozen or so uS).
Repeat main loop.
Interrupt handler:
If falling-edge on RB0/INT0, then output a 1 mS pulse on RB3.
In step 3, the ‘certain value’ determines the output V of the boost circuit, which is set to 760V for a 7616 tube.
interesting… the GM tube used in a Geiger counter product we manufacture for a scientific school supplier runs on about 525V. Are your higher voltage tubes detecting a different type of particle or is it just a matter of the physical design and what it takes to ionize the particular gas in the tube?
I’m not an expert in G-M tubes, but with ‘modern’ tube types the range seems to be 500-700 V for most of them. A popular smallish tube is an LND 712 - specs here: lndinc.com/gm/gmend.htm
Meanwhile, the “cold war” tubes are mostly 700-800V (examples are 5979 and 5980, used in zillions of military counters).
Tubes from the 30’s and 40’s tend to be 1000 V and higher, I think.
Over in the SparkFun forum, someone pointed out that the Feb issue of Everyday Practical Electronics has a PIC-based Geiger counter project in it. It has an LCD display, a USB port, and uses an LND 712 tube.
BTW, I don’t think there’s any correlation between anode voltage and the type of particle being detected.
My basic understanding of the particles is this:
Three main types are alpha, beta, and gamma, in increasing order of energy. Alphas are electrons, Betas are protons, and Gammas are neutrons (or something like that).
Only the more sensitive tubes can detect alphas, because they can barely penetrate the tube envelope. An alpha-detector tube usually has a ‘window’ made of a very thin sheet of mica (like .0005").
Gammas go right through nearly anything - it takes several inches of lead to stop them reliably.
Some sources of radioactive materials:
Watches made from the 30’s to the 60’s can have radium dials. It’s radium mixed with a phosphor. Over the years, the radiation tends to break down the phosphor, so it doesn’t ‘glow in the dark’ anymore, but the radium will continue to be active for a LONG time.
Most household smoke detectors have Americium 241 in them, which is a good alpha emitter.
Some old military electronics equipment has dial-markings that use Radium or something similar, just like the old watches.
An old brand of dishes called “FiestaWare” used to be made with an orange glaze that is full of Uranium ore. (FiestaWare also came in other colors, which are NOT radioactive).
There’s a type of antique glassware called “Uranium glass”, which is (duh) radioactive.
Alpha Radiation-(Sub script 2 super script 4 in front on He) Protons they are so big it it easy to stop them ei: a sheet of paper will do fine
Beta Radiation- (B- (the - is a super script)) Electrons, much smaller than the protons, are harder to stop ei: a few inches of lead
Gamma Radiation- (cant explain sign ) No mass, this form of radiation is pure energy i think, making it the hardest to stop, ex: a foot or 2 concrete, or 1/2 foot-foot of lead
didn’t mean to go into it so much, but chemistry is one thing im good at
not sure on the exact amount of material it takes to stop it except for alpha the others are just educated guesses
Some quick research on the net:
Chunga is mostly right. Alphas are 2 protons and 2 neutrons, making them the same as a helium nucleus. They are the most dangerous of the group, because they very readily cause changes when they bump into organic molecules. But since they won’t penetrate your outer skin layers, it means that they are typically only dangerous if you inhale or eat alpha-emitting materials.
Betas are like electrons. They are somewhat dangerous because of their negative charge.
Gammas are not particles at all, but rather waves, like light/photons. I think the danger with gammas is that they can cause the release of other types of radiation when they bump into things.
…now, if only u had something radioactive…
) No mass, this form of radiation is pure energy i think, making it the hardest to stop, ex: a foot or 2 concrete, or 1/2 foot-foot of lead