After a day filled with business meetings | didn't want to risk killing the DC/DC converter for good, and I decided to look a little closer at one of the new arrivals from China, small and cheap voltmeter ($1.12 including shipping).
Repetitio non placet they say, but this voltmeter turned out to be really nice:
The LED display 3361BS is "0.36", red, common anode". The internal supply voltage is a bit unusual (3.0V), but otherwise the module is very hackable.
The 6 pads with 1.27mm pitch to the left are connected to the following signals:
1 SWIM (7S-LED segment D) 2 TxD 3 RxD 4 NRST 5 +Ub 6 GNDThe STM8S003F3P6 pins are assigned as follows:
|STM8S003F3P6||assigned to||STM8S003F3P6||assigned to|
|1 PD4||7S-6 (NC!)||20 PD3||7S-5 G|
|2 PD5||Pad2 TxD||19 PD2||7S-4 C|
|3 PD6||Pad3 RxD||18 PD1/SWIM||7S-3 DP, Pad1 SWIM|
|4 NRST||Pad4 NRST||17 PC7||7S-2 D|
|5 PA1||7S-9 Digit 2||16 PC6||7S-1 E|
|6 PA2||(7S-9 Digit 2)||15 PC5||7S-7 B|
|7 Vss||GND||14 PC4/Ain2||TP (535k-Ain-8k26-GND)|
|8 Vcap||C||13 PC3||7S-12 Digit 1|
|9 Vdd||+3.0V||12 PB4||7S-10 F|
|10 PA3||7S-8 Digit 3||11 PB5||7S-11 A|
I guess that the designer was bored by making yet another cheap Chinese
voltmeter, and he decided to make a hackable voltmeter instead. If not, why would one expose not only SWIM/NRST but also RxD and
TxD? Why route a spare GPIO to the (unpopulated) NC pad of the LED
Hat-tip to China!