Category
Other
Hardware
Heltec Mesh Node T114
Firmware Version
develop
Description
During power consumption measurements on my Heltec T114 i realized that the module consumes 2.9mA after initializing cpuDeepSleep(portMAX_DELAY), which also happens after every shutdown (eg. by software or buttons).
The reason is that #7882 enables the ADC to monitor the battery voltage after power down. This drives ADC_CTRL to high and results in a consumption of 2.9mA on Heltec T114, because the resistor used at the base of the transistor is 1kOhm. (3.3V / 0.0029A = 1138 Ohm).
The drain calculates:
Base current through R9: I_B = (3.3−0.7) V / 1 kOhm ≈ 2.6 mA
Resistive bleed through R25: I_R25 = 3.3 V / 10 kOhm ≈ 0.33 mA
Total drawn from ADC_Ctrl ≈ 2.6 mA +0.33 mA ≈ 2.93 mA
Which perfectly matches the measurement.
The only affected board variant is the Heltec T114 because, aside from the unproblematic RAK 4630, it is the only one that had BATTERY_LPCOMP_INPUT defined, which enables ADC monitoring of the battery during the shutdown state.
A suggested fix is in #8800.
Category
Other
Hardware
Heltec Mesh Node T114
Firmware Version
develop
Description
During power consumption measurements on my Heltec T114 i realized that the module consumes 2.9mA after initializing
cpuDeepSleep(portMAX_DELAY), which also happens after every shutdown (eg. by software or buttons).The reason is that #7882 enables the ADC to monitor the battery voltage after power down. This drives ADC_CTRL to high and results in a consumption of 2.9mA on Heltec T114, because the resistor used at the base of the transistor is 1kOhm.
(3.3V / 0.0029A = 1138 Ohm).The drain calculates:
Base current through R9: I_B = (3.3−0.7) V / 1 kOhm ≈ 2.6 mA
Resistive bleed through R25: I_R25 = 3.3 V / 10 kOhm ≈ 0.33 mA
Total drawn from ADC_Ctrl ≈ 2.6 mA +0.33 mA ≈ 2.93 mA
Which perfectly matches the measurement.
The only affected board variant is the Heltec T114 because, aside from the unproblematic RAK 4630, it is the only one that had
BATTERY_LPCOMP_INPUTdefined, which enables ADC monitoring of the battery during the shutdown state.A suggested fix is in #8800.