Datalogger Bolt-On For Mighty Ohm Geiger Counter - Page 1
Forum section: electronics / projects

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 12:36:17 pm
content: I have been thinking about this for a while, although the mighty ohm geiger counter does have serial output you need a laptop to record its data. The counter provides a 3v pulse output which is triggered every time there is a detection so i just need the board to count and record.I have done quite a bit of thinking about how to do this and have a few ideas which would work but thought i'd see what other ideas might come from the forum... it might help me make some decisions about how to proceedmy requirements:direct plug in to the geiger counterpowered by the geiger counters two AAA batteries (low power battery operation)records CPM (counts/min) with current hours, minutes, date to non-volatile memorysome way to extract data back out, like serial, SD card etcdisplay not requireddeep memory, i think around a week or so before its full would be niceDepending on how much spit and polish i decide to lavish on this i might make kits availableGeiger Counter website:http://mightyohm.com/blog/products/geiger-counter/

author: dannyf
author_rank: Super Contributor
timestamp: February 19, 2014, 02:04:21 pm
content: Something like this may work:1) mcu mostly in sleep;2) it wakes up once a minute (thus needing a LF oscillator that works in sleep), save counts / time elapsed in minutes to media;3) need a counter or interrupt to count the pulses while in sleep.Depending on your memory needs, it is likely a few bytes per minute x the number of minutes required. No SD card if you can write to flash from an internal buffer.Likely not difficult.

author: SpectrHz
author_rank: Contributor
timestamp: February 19, 2014, 03:22:56 pm
content: This is something I have been thinking about as well, as having flying cables for serial data is quite inconvenient, and the plexiglass rear panel could be easily retrofitted with a board..

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 03:25:04 pm
content: thanks danny, very similar to my initial thoughts.i have used i2c & spi serial eeproms before, which are nice and cheap but any thoughts on other alternatives for serial access nv storage?i have written directly to SD cards before using spi but i would prefer to avoid them for this.

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 03:29:56 pm
content: Quote from: SpectrHz on February 19, 2014, 03:22:56 pmhmm, i was thinking something that sat on the front panel that plugs down directly onto the pin headers, but i like the idea of a 2nd board on the back, it would certainly give me lots of space to work with.This is where i need to decide if i am to just hack something quick and dirty on strip board just for my own use or make something proper!

author: dannyf
author_rank: Super Contributor
timestamp: February 19, 2014, 03:41:21 pm
content: The simplest hardware solution would be external eeprom or fram. Assuming com less than 64kcpm, and 45 day max duration, you need 4 bytes per minute. 240 bytes per hour, 6kb per day, 300kb to max out.so if you are talking about days or a few weeks, you can use eeprom or fram. More than that, flash self programming or SD card is the way to go.

author: georges80
author_rank: Frequent Contributor
timestamp: February 19, 2014, 05:31:59 pm
content: Seems like you are trying to sleep the uC and all sorts of contortions to save current.How are you powering the geiger counter and how much does it draw over an hour (assuming some average 'ticks')?Running a uC (AVR are my preference) on a 32khz crystal will be very low current (provides you an easy clock) and you don't need to sleep etc etc. SPI eeproms are cheap and easy to find in mbit size. Bit of power management to power down the interfaces you don't need whole logging and you should be well under 1mA without any effort.cheers,george.

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 05:47:34 pm
content: Quote from: dannyf on February 19, 2014, 03:41:21 pmi have used fram and eeprom before, fram is probably a bit overkill for this as i wont need to write lots of data in a short time (fram is great at fast writes).Biggest problem is storing the date and time, of course i cant assume the device is going to be on in one continual cycle so i will have to store the date & time along with each datapoint. It might be on for 4 hours one day or 2 days etc. I could come up with some creative code to log the time of a cycle with the number of points. Given i want to keep this as simple as possible at the moment i might opt for just lots of storage and keep the data as flat as possible.

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 05:49:20 pm
content: Quote from: georges80 on February 19, 2014, 05:31:59 pmdont know it's standard current consumption, but it's been running on it's original 2 AAA alkaline batteries for a long time. When my uCurrent arrives i will have to measure it properly! But it does have good battery life at the moment so i dont want to turn it into a battery eating monster.

author: georges80
author_rank: Frequent Contributor
timestamp: February 19, 2014, 05:57:03 pm
content: I presume you have a 1/2 decent meter, you should be able to easily measure down to sub milliamp levels.cheers,george.

author: georges80
author_rank: Frequent Contributor
timestamp: February 19, 2014, 06:10:16 pm
content: http://mightyohm.com/forum/viewtopic.php?f=15&t=51010mA if it's the same as yours, so actually a LOT of current compared to a uC and an SPI eeprom (which would easily be well under 1mA running even at a few MHz).You don't need to wait for you ucurrent to measure 10mA!!cheers,george.

author: dannyf
author_rank: Super Contributor
timestamp: February 19, 2014, 06:42:58 pm
content: Quoteanother approach is to store time once a given number of pulse counts have been reached. This works if your interest is primarily in the high pulse count periods.It is a huge space saver when pulse counts are minimum; however, if counts are coming fast and furious, you could end up taking more space.A hybrid is also possible: store time when pulse count is low; store pulse count in a given period of time when pulse count is high.

author: dexters_lab
author_rank: Unknown
timestamp: February 19, 2014, 07:56:02 pm
content: just measured quickly on my bench psu, saying approx 7ma idle peaking to about 15ma when i stick some 4500 count uranium next to it!so i probably dont need to worry too much about power, just some basic power management and a low clock on the uC should be enoughJust done some quick calcs and even if i store the date & time in the most wasteful lame format for every minute with a 32 bit number for the counts i will still get 11 days of continual log data from a 1mbit eeprom that costs less than £2will brush the dust off my pic development board at the weekend