Differences

This shows you the differences between two versions of the page.

--- projects:blinker:work_logs:6_power_consumption_testing [2022/02/27 12:12] – tjhowse
+++ projects:blinker:work_logs:6_power_consumption_testing [2022/03/06 22:33] – tjhowse
@@ Line 10: / Line 10: @@
 I want to measure the voltage over time as the device discharges so I can calculate how much power each component uses. I will run the following tests:
-  * JP1 open, disconnecting the LED and microcontroller,
+  * JP1 open, disconnecting the LED and microcontroller from the supercaps,
     * This should measure the self-discharge and leakage across the Zener D2.
   * JP1 closed, running unoptimised naive code, blinking the message "ss s"
@@ Line 47: / Line 47: @@
 After optimising the code to disable unused peripherals and enter deep sleep between blinks, using the watchdog timer to wake to process the next frame, I was able to reduce power consumption to very close to the passive drain of the system. This represents roughly a 95% improvement in energy efficiency over the naive approach.
+====== Isolating sources of lost energy ======
+I wanted to confirm the source of my passive losses. I suspect the voltage limiting Zener diode. It's sized to handle sinking a reasonable amount of current (around 100mA) to ground to avoid overcharging the capacitors. The bigger the Zener, the more leakage. The datasheet of the one I'm using (MM1Z2V4, I think. JLC part C96629 isn't in their catalogue anymore and I didn't store the actual part number anywhere...) specifies a 120µA leakage current at 1V, which is in the right ballpark. I re-ran the passive discharge test but with a supercap charged directly from my benchtop supply and got a big surprise:
+{{:projects:blinker:work_logs:pasted:20220306-223145.png}}
+The isolated capacitor (green line) discharged even faster than the identical one in the circuit, leaking across the Zener! What?
+I assumed there was a difference in my experimental setup. I ran the test again, but this time I charged the second capacitor by connecting it to the circuit
 ===== Video =====
 {{ youtube>WTbTDbBAby0?large }}
 ===== Next Time =====
-I don't think there's much point in trying to further improve energy efficiency of the code. The next steps might be adding features like multiple message sequences.
+I don't think there's much point in trying to further improve energy efficiency of the code. The next steps might be adding features like multiple message sequences, and/or improving the space efficiency to fit more/longer messages.
 [<6>]