BS2P40 Power considerations, "Queuing" readings to save power, and a 40 pin "Do
WBA Consulting
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From my recent Temperature Datalogger project (http://forums.parallax.com/showthread.php?p=792332) using the BS2P40 and VMusic2 (sister to the 27937 USB datalogger), I came across a few things that I want to clarify with others.
1)I used a 9 volt battery and a 7805 to provide 5 volts for all devices. I ran the 5 volt output from the 7805 to Vin on the BS2P40 and I believe that is incorrect. If I supply 5 volts, I should connect it straight to VDD and leave Vin unconnected, right?
2) What is the most common way or most efficient way to power a BS2P40 (or other stamp) for portable applications? 9 volt? Two AAs with a boost circuit? other? The 9 volt battery in my project only lasted about 5,000 readings.
3) Is there an easy way for me to queue up my readings so that I can power down the VMusic2? It would be nice to store about 5 minutes worth of readings (60 @ once/5 seconds) and then blast them into the VMusic2 all at once. Should I add an EEProm to store the readings then dump the EEProm into the VMusic2 at 5 minute intervals?
4) I was pretty happy with how my 35 minute build ended up on the proto board. However, I though that it would be nice to create a 40 pin socket module that has a 4 pin header to attach a DB9 for the serial port, a 5 volt power circuit of some sort, and headers for all the I/O pins to make it easier to attach items. The socket would still work normally if placed in the PDB, etc. Any thoughts on that?
thanks in advance,
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Andrew Williams
WBA Consulting
IT / Web / PCB / Audio
1)I used a 9 volt battery and a 7805 to provide 5 volts for all devices. I ran the 5 volt output from the 7805 to Vin on the BS2P40 and I believe that is incorrect. If I supply 5 volts, I should connect it straight to VDD and leave Vin unconnected, right?
2) What is the most common way or most efficient way to power a BS2P40 (or other stamp) for portable applications? 9 volt? Two AAs with a boost circuit? other? The 9 volt battery in my project only lasted about 5,000 readings.
3) Is there an easy way for me to queue up my readings so that I can power down the VMusic2? It would be nice to store about 5 minutes worth of readings (60 @ once/5 seconds) and then blast them into the VMusic2 all at once. Should I add an EEProm to store the readings then dump the EEProm into the VMusic2 at 5 minute intervals?
4) I was pretty happy with how my 35 minute build ended up on the proto board. However, I though that it would be nice to create a 40 pin socket module that has a 4 pin header to attach a DB9 for the serial port, a 5 volt power circuit of some sort, and headers for all the I/O pins to make it easier to attach items. The socket would still work normally if placed in the PDB, etc. Any thoughts on that?
thanks in advance,
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Andrew Williams
WBA Consulting
IT / Web / PCB / Audio
Comments
2) This relates to item 3, being able to power down devices that gobble power, like the vmusic2. No best answer on the battery. How about a rechargeable 6.4 volt (2 cell) LiFePO4 battery? The 7805 is not the most efficient regulator available. For this application, you really do best with a regulator that offers low quiescent current and low dropout voltage.
3) How about the eeprom or scratchpad on the BS2p itself as a buffer? The scratchpad at 128 bytes in enough for 60 readings. Or, there is enough eeprom available to make a circular buffer so that repeated writes don't wear out one small section. The BS2pehas an extra 16 kbytes of eeprom for data storage, and overall it is the best bet for a low power data logger.
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Tracy Allen
www.emesystems.com
1)Clarification appreciated.
2) I am thinking my best solution is changing away from USB and using SD. That should save a lot of power. I am also looking into using the LD1117 instead of the 7805.
3) I took a look at the BS2pe and I added one to my wishlist. That seems to be a much better solution for datalogging.
3) I'll start my EEProm usage learning From the datalogger appnote link on the BS2pe page. Then I'll dig into the manuals, etc. I never had much use for EEProm before so I hadn't even though of buffering the data there.
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Andrew Williams
WBA Consulting
IT / Web / PCB / Audio