Digi-Key
Topics: ADC, Brownout Detection, LF RFID
Transcript Excerpt
Users are ready to run art projects on two AAA batteries for a year. When a User reduce the power supply voltage which mimics 2 AAA batteries to below 1.95 volts, Users see the 328 P start to reset repeatedly. It just drains the batteries faster. The best solution is to turn off the Brownout Detection. The next best thing User came up with is to measure the battery voltage transmitting whenever it falls down a point The good part is Users can turn off the Brownout Detection. However, Users can use the 1.9 volts from regulator. To start need to disable the Brownout Detection. Connect the bear 328 Kitaura. Make sure to select the mini core 328 P selected with a 1-megahertz internal clock. Arduino as ISP is selected and click tools, the battery voltage should be higher than the regulated 1.9 Volt. User can calculate the voltage drop across the collector and emitter of the PNP, but it’s easier just to find the ADC number. Users are using a 1/2 voltage divider. User added divider control pin and 80CA0 pin which enable in setup by disable the ADC. Then Users will discard the first ADC reading to let the reference voltage settle and take an ADC reading. User just go back to sleep before calling go to sleep function. Users know this is going to be longer than four seconds. So, Users change the watchdog timeout. The maximum watchdog timeout is 8 seconds. User will also create a wake up counter global variable and set to the Max wake up. There’s really eight seconds between wake ups. There are two distinct periods first is the transmission and followed by several cycles of sleep. Users need to figure out how many eight seconds sleep cycle need to run on two AAA batteries for a year and ADC reading. First, figure out how long our total transmit. Then figure out the proportion that each current draw section is active. Multiply that proportion by the current draw at each of these sections to get the average current draw. User then use that to calculate the total time for one transmit and one sleep cycle. Their expected total average current draw is user transmit 73.6 milliseconds out of total cycle time. Multiply that by transmit current, then use 8 * 8 seconds sleep time divided by total cycle time to get the proportion of time that users sleep. Users see that expected average current draw is .0997 milliamps right at 100 microamps. Users successfully designed a system without turning off Brownout detection. Users went for a long time without testing. Users will connect two AAA batteries to device then see the first reading come in and start a timer a little over a minute later get the second reading. The final form of code can be found in Laurel weather GitHub repository. Remember that because of that radio, if user plan to put this device into an enclosure and sell it in the United States, at least Users need FCC certification.
