Adding a Digital Counter to an Analog Geiger Counter
Posted: Sun Dec 03, 2017 10:05 am
Since I have some time due to the fact that my fusor is down for cathode repairs and the new neutron detector is stalled for the same reason - i.e. no neutrons to test with - I decided to finish another small project that I have wanted to do for awhile. I have an old, surplus Ludlun analog Geiger counter. It had many issues so getting it for $10 wasn't a surprise. The batteries had to be drilled and chiseled out; the damage to the battery case was so bad that I gave up on getting it to work as designed and instead, simply drilled the case so I could wire in an external battery pack. Also,I had to replaced a voltage regulator chip and fixed some wires (a few were too frayed and their soldier connections were failing.)
I bought a $7 dollar (free shipping) Chinese made "counter" module - these are small, self contained, have a permanent internal battery and only need to add a reset switch. I wired the unit from the Ludlum's 'speaker' posts on the circuit board and connected these to the simple counter (polarity does matter.)
When the Ludlum is counting, the digital display follows the counts. The Ludlum analog meter indicated about 700 counts a minute and the digital meter recorded 753 counts in a minute. So, works well. Since the Ludlum's internal battery holder is empty, I installed the counter in this location. I cut a small piece of plastic to act as a mounting panel for the counter. The entire effort took less than two hours (including the first, bench test before I modified the Ludlum - wanted to make sure the idea worked.)
The micro-switch to the left of the digital meter re-zero's the counter's display.
I decided to do this because at some future day, I might convert this Ludlum into a neutron counter - it has the required comparator, totalizer, and a good input amplifier (I can add an external pre-amp if necessary.) All it lacked was a decent digital meter (neutron detectors rarely provide more than a few tens to up to a hundred or so counts a minute for a fusor. Hence, a digital display is necessary to read such a low count source with such a device.) Now that I have an interface box that allows the required high voltage to be applied to the neutron tube, but steps down that voltage to a safe range that the Geiger counter can handle, so this project is actually viable.
Besides, the digital display is a nice extra feature to have: both an analog meter and a totalizing digital display on the old Ludlum. Besides, for low count situations, this is useful added feature. Another nice feature is I can calibrate the analog meter to more accurately match the count rate - that is, with my known source (about 1200 Beta counts/min; I can now set the analog meter to reflect this count rate. (Not a true calibration but a useful manner to set this analog meter to at least match the count rate.)
For those with a working battery case, the digital counter can be mounted on the side of the case - cutting might be a bit involved. Or, a small external mounting bracket could easily be installed.
This was a far easier project than I at first thought and very inexpensive. The cheap counter module works very well with the speaker output of the Geiger counter; simple to splice into the circuit, too. Also, I was pleased by its excellent performance to the applied signals from the speaker circuit - hope the internal battery lasts a good while.
Below are pics of the meter and counter and the internal wiring running from the circuit board to the battery 'case'. I reused the existing battery contact points in the event I ever fixed its problems.
I bought a $7 dollar (free shipping) Chinese made "counter" module - these are small, self contained, have a permanent internal battery and only need to add a reset switch. I wired the unit from the Ludlum's 'speaker' posts on the circuit board and connected these to the simple counter (polarity does matter.)
When the Ludlum is counting, the digital display follows the counts. The Ludlum analog meter indicated about 700 counts a minute and the digital meter recorded 753 counts in a minute. So, works well. Since the Ludlum's internal battery holder is empty, I installed the counter in this location. I cut a small piece of plastic to act as a mounting panel for the counter. The entire effort took less than two hours (including the first, bench test before I modified the Ludlum - wanted to make sure the idea worked.)
The micro-switch to the left of the digital meter re-zero's the counter's display.
I decided to do this because at some future day, I might convert this Ludlum into a neutron counter - it has the required comparator, totalizer, and a good input amplifier (I can add an external pre-amp if necessary.) All it lacked was a decent digital meter (neutron detectors rarely provide more than a few tens to up to a hundred or so counts a minute for a fusor. Hence, a digital display is necessary to read such a low count source with such a device.) Now that I have an interface box that allows the required high voltage to be applied to the neutron tube, but steps down that voltage to a safe range that the Geiger counter can handle, so this project is actually viable.
Besides, the digital display is a nice extra feature to have: both an analog meter and a totalizing digital display on the old Ludlum. Besides, for low count situations, this is useful added feature. Another nice feature is I can calibrate the analog meter to more accurately match the count rate - that is, with my known source (about 1200 Beta counts/min; I can now set the analog meter to reflect this count rate. (Not a true calibration but a useful manner to set this analog meter to at least match the count rate.)
For those with a working battery case, the digital counter can be mounted on the side of the case - cutting might be a bit involved. Or, a small external mounting bracket could easily be installed.
This was a far easier project than I at first thought and very inexpensive. The cheap counter module works very well with the speaker output of the Geiger counter; simple to splice into the circuit, too. Also, I was pleased by its excellent performance to the applied signals from the speaker circuit - hope the internal battery lasts a good while.
Below are pics of the meter and counter and the internal wiring running from the circuit board to the battery 'case'. I reused the existing battery contact points in the event I ever fixed its problems.