Hi Guys,
I'm a big fan of yours, very impressive solutions and amazing support. One thing I couldn't find on the forums is what is the best way to create a battery powered standalone datalogger? I need to measure some current and voltage signals (AC and DC), log the results, and be able to run for 2 weeks without a recharge. I have the suitable (hall-effect) current sensors ready, the voltage signals would only be resistive dividors with precision resistors.
Could you give us some figures on what is the average current draw of the T4 or the U3 dataloggers?
I have a couple of ideas, but I don't know what is the best implementation. I'm considering now three options;
- I know the T7 is the classic datalogger, it can run independently and save results to a micro-SD card, but it's too bulky and pricey for our application.
- I'm considering connecting a small Raspberry Pi zero to the T4/U3 and let that handle the datalogging, I'm just somewhat worried about it's power consumption (~0.4W, so ~130 Wh in a two week period).
- I'm considering writing a LUA script to T4 and send the processed packets via UART/SPI to an external MCU with an SD card like this: https://www.sparkfun.com/products/14001. This is probably the lowest energy budget and cost option.
I'm also open to any other suggestion on how to implement this. Basically the bipolar voltage signal is creating the complexity that necessitates a high-end bipolar ADC. Let me know what you guys recommend.
Thank you for your answer in advance.
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The T4 pulls about 200 mA. The U3 pulls about 50 mA. The T7 can power down various features to get to ~10 mA. If you are trying to keep costs down then a U3 with a Pi is probably the way to go, as long as the power requirements can be met.
Your idea of using a T4 and a separate SD card file system sounds good too, but the T4's power draw may be an issue.
From a power standpoint the T7 looks like the best fit.
Great, thank you for the quick answer. I'll try to use a U3 HV and a raspberry pi zero, then we'll see how it goes. Just to be safe, I also ordered a T4.
Are there some form of power-down options for the U3 and the T4? Like for the T7? Or like an enable pin? Alternatively I'm considering cutting the power altogether, when it's not in use.
"... power-down options for the U3 and the T4?"
The T4 can shut off its LEDs. The U3 does not have any low-power features.