ATtiny Microcontroller for Processing

The ATtiny5 is a low-power 8-bit microcontroller integrate circuit (IC) manufactured by the Atmel Corporation. It is a tiny chip available in a SOT23-6 package with a footprint measuring 3 mm × 3.04 mm. A useful feature of this chip is that it has an 8-bit analogue-to-digital converter (ADC) circuitry built-in, together with a comparator op-amp. This IC has a powerful instruction set consisting of 54 instructions, which is sufficient for any type of statistical algorithms such as calculating the half-life. It can process 12 million instructions per second, whilst operating at 12 MHz. It has 32-bytes of internal SRAM, and 1024 bytes of flash memory that is programmable through an ISP.

ATtiny5 Circuit Diagram

In order to perform the statistical calculations a very powerful and a very small microcontroller was required. This 8-bit AVR based on advanced RISC architecture seems to be the right choice.

I figured that this was the perfect IC for this application as it is just the right physical size, with the processing capacity to calculate the half-life. The output from the ionisation chamber feeds the internal onboard ADC through PB0, and one of three LEDs lighting determines the result of the statistical analysis.

Program Code

The program first measures the background radiation within a set period, and then the radioactive sample is measured. It calculates the half-life several times in succession and then extrapolates the result to determine if it is polonium.

ADC

The analogue-to-digital converter (ADC) reads pin 1 (PB0) for a dc value. It has an 8-bit resolution with a 65 µs conversion time, which is adequate for this application. The signal input voltage range is 0 V to 5 V.

LED Output Result

The output result from the program code lights one of three LEDs. The NTE30011, NTE30012, NTE30013 are surface-mount LEDs which are 3 mm in size. The series resistance values can be easily calculated using my online calculator.

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