Figure 7 Analog Digital Meter (ADM)
When I first thought of doing this project, I tried mounting my standard 16x2 character LCD. This LCD meter display was too large to fit into the space allocated for the front panel meter. So I designed a new PC board that uses a smaller 8x2 character LCD to create an Analog Digital Meter see figure 7. The 8x2 LCD fits nicely into the allocated meter space.
The smaller LCD presented new challenges regarding the display of information from the Geiger Counter. When using the 16 x 2 LCD display I had plenty of space to place the Count Per Second (CPS) on the top line and the equivalent radiation level in mR/hr (or mSv/hr) on the second line. In addition to this I wanted something that would replace an analog meter. I wasn't happy with the available analog meters or the electronics to implement them, so I decide to create my own.
The space allocated on the LCD's 8 character line doesn't permit me to write mR/hr, so I shorten this to mR. This left 5 characters to display the radiation level. I took a similar approach to displaying CPS. This left 4 character to display a CPS numerical value up to 9999, more than enough.
The second line of the 8x2 LCD is a dedicated analog power meter. To create the LCD analog meter I programmed 8 customer characters into the LCD. Each character represents a binary number: 1, 2, 4, 8, 16,32, 64 and 128. The chart below, see figure 8, provides an indication of how to read the power meter. Using the information we can obtain a reasonable approximation of CPS from 1 CPS to 2040 CPS from the second line of the Analog-Digital Meter. The chart below illustrates the CPS range capabilities of the ADM meter.