ES32C14 technical support

Hello, I'm building a prototype using the ES32C14 expansion board (12/24V version) with an ESP32-WROOM-32D module, and I have a few technical questions your team may be able to help with. I do have the board's schematic (rev 1.0, dated 2023-07-13), but some details aren't legible or aren't shown on it.

1. Optocoupler part number (Input bank IN1-IN4)
The schematic labels these only as "OPT1"-"OPT4" with no visible manufacturer/part number. Could you tell me the exact optocoupler model used on these 4 NPN digital inputs? I need to confirm its maximum reliable switching frequency — I'm reading a flow sensor pulse signal at up to ~750Hz through one of these inputs (IN4) and need to be sure no pulses are lost.

2. Input polarity
For the IN1-IN4 opto-isolated inputs: when an external NPN sensor is active, does the corresponding ESP32 GPIO read HIGH or LOW? (i.e., is the output active-high or active-low with the internal pull-up?)

3. Relay ratings
The schematic identifies the relays as Songle SRD-12VDC-SL-C. Can you confirm the actual switching rating you use in the datasheet for this board — specifically the DC switching rating (I'll be switching a 12VDC motor load, not AC), and the board's ambient operating temperature range?

4. GPIO12 / relay CH3
I noticed CH3 (relay output) is wired to ESP32 GPIO12, which is a flash-voltage strapping pin on boot. Is there any pull resistor or default state on that relay driver circuit that could interfere with the ESP32's boot sequence?

5. Analog current input calibration (Ii1/Ii2)
For the 0/4-20mA current inputs (Ii1 = GPIO34, Ii2 = GPIO35): what raw ADC count (0-4095) corresponds to 4mA and to 20mA on the onboard signal conditioning circuit? I'd like to cross-check this before bench-measuring it myself.

6. Full datasheet
I saw there's a datasheet download (ES32C14-1.rar) linked from one of your distributors, but I wasn't able to open/extract it. Could you send me the datasheet directly, or a PDF version, if available? A complete GPIO-to-terminal pinout table would be extremely helpful even just to double check what I've already derived from the schematic photo.

Thank you very much for your time — I understand this board doesn't come with full technical support, but any information you can share would help a lot for this project.

Answer :

1 The optocoupler used is the EL817.
2 The ESP32 GPIO reads a low level.
3 You can check the datasheet for the SRD-12VDC-SL-C here: https://www.alldatasheet.com/datasheet-pdf/download/1131793/SONGLERELAY/SRD-12VDC-SL-C.html
4 No toggling was observed on CH3 during power-up in testing, nor did it interfere with the startup sequence.
5 This depends on the code you write.
6 https://1drv.ms/u/c/f5c7cfff112f0ffe/Ef4PLxH_z8cggPWcSAAAAAABv2qQ5NT1EVC_lNHpa4C25Q?e=MFShcq