Decades ago, when a customer found that my Tera Ohm Meter expensive, He suggested the specs for this low cost scaled-down model. This was found useful for people sub-contracting Telecom Equipment Manufacturing.
Here are some Test and measurement notes. These ideas come from practical experience. But the jots are not in any order but are quite important.
The LM3914 is a monolithic integrated circuit that senses analog voltage levels and drives 10 LEDs, providing a linear analog display. A single pin changes the display from a moving dot to a bar graph. Current drive to the LEDs is regulated and programmable, eliminating the need for resistors. This feature is one that allows operation of the whole system from less than 3V.
The circuit contains its own adjustable reference and accurate 10-step voltage divider. The low-bias-current input buffer accepts signals down to ground, or V–, yet needs no protection against inputs of 35V above or below ground. The buffer drives 10 individual comparators referenced to the precision divider. Indication non-linearity can thus be held typically to ½%, even over a wide temperature range.
My LM3914 Circuits
Millivolt Meter using a LM3914 LED Dot Display
Rechargeable AA cells are very popular for a large variety of portable applications. The number of brands is also high, and the cell quality can differ considerably. Cell capacity is sometimes different from that specified, and the capacity often deteriorates dramatically after a limited number of discharge cycles. ….
See Maxim Application Note – Simple Characterization Circuit for Rechargeable AA Cells
This characterization circuit, plus a PC and some software, accurately measures the full discharge cycle for a rechargeable AA cell. Cell capacity and output resistance can easily be determined from the curve resulting from these measurements.
In Figure 1, the simple circuit is connected to the USB port of a PC. No external power source is required because power is extracted from the USB bus voltage. U1 (DS9490R) is a USB dongle that converts the USB protocol to the 1-Wire® protocol, thereby allowing the PC to communicate with the key circuit component (U2).