Maxim DS1803 Digital Potentiometer

This is just a note to remember to use this cool chip one day.

http://www.nearfuturelaboratory.com/2008/07/07/ds1803-digital-potentiometer/

Texas Instruments TLC2554ID

This is just a note to remember to use this cool chip one day.

Product page

Calculate internal battery resistance

Battery internal resistance forms a divider with external load.
So to calculate internal resistance, take those steps :

• measure the battery voltage without load (Vnoload)
• measure again with a resistor of RloadΩ attached (the lower ohm value, the better, but watch outfor power ratings !), you have a difference with previous measurement (Vdrop)

The battery internal resistance is then :

Real world example on AA :

Thus :

Since my metter has a milliVolts resolution, we just have a range between 0.001 and 0.003 for Vdrop.
So Rbattery can be anything between 0.33Ω and 1Ω.

Short-circuit current for this AA battery would be somewhere between 1.421/0.33 = 4.33A and 1.421/1 = 1.42A
Mesasurement made, it is around 4.2A. Watch out for your metter current rating if you do this. Some batteries have a much lower internal resistance.

Microchip MCP23S08

This chip is a 8-bits port expander driven by SPI (or I2C for MCP23008 version).

Microchip MCP23S08 datasheet