Print PDF
Favorite
Email
Step 5Voltage Meter
As if we hadn't sunken to the depths of geekerie with a binary watch, we slap on a voltage reference and input pin to make a voltage meter.
The voltage reference is the Microchip MCP1525. This is a 2.5 volt reference with an operating range of 2.7 to 10+ volts. In the pictured watch the TO-92 package is used, though future watches will use the surface mount version (SOT-23). The reference is powered by a PIC pin so it can be turned off to conserve power.
At this point we can measure up to 2.5 volts using the PIC's Analog Digital Converter. We take this a step further and add a resistor voltage divider to the multimeter input. Using two resistors (100K/10K) we divide the input voltage by 11 giving a new input range of ~30 volts. This is a good point that encompasses all the low voltages we are likely to encounter (1.2/1.5 volt batteries, 3 volt coin cells, 5 volt logic, 9 volt batteries, and 12 volt power rails). A 22Kohm resistor could be substituted for the 10K resistor giving a smaller range but higher resolution. The spreadsheet included with this instructable can help you choose resistor values.
Ground and measurement probes connect to the programming header at the back of the watch.
MCP1525 Details:
http://www.microchip.com/stellent/idcplgidcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en019700
The voltage reference is the Microchip MCP1525. This is a 2.5 volt reference with an operating range of 2.7 to 10+ volts. In the pictured watch the TO-92 package is used, though future watches will use the surface mount version (SOT-23). The reference is powered by a PIC pin so it can be turned off to conserve power.
At this point we can measure up to 2.5 volts using the PIC's Analog Digital Converter. We take this a step further and add a resistor voltage divider to the multimeter input. Using two resistors (100K/10K) we divide the input voltage by 11 giving a new input range of ~30 volts. This is a good point that encompasses all the low voltages we are likely to encounter (1.2/1.5 volt batteries, 3 volt coin cells, 5 volt logic, 9 volt batteries, and 12 volt power rails). A 22Kohm resistor could be substituted for the 10K resistor giving a smaller range but higher resolution. The spreadsheet included with this instructable can help you choose resistor values.
Ground and measurement probes connect to the programming header at the back of the watch.
MCP1525 Details:
http://www.microchip.com/stellent/idcplgidcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en019700
| « Previous Step | Download PDFView All Steps | Next Step » |
 |
Add Comment
|
