I have a few no-name 40khz ultrasonic distance sensor modules (HC-SR04) laying around.
I purchased them a few years ago, but they still seem to be for sale.
They appear visually similar to the original sensor module.
I thought I might scope some on board signals and maybe Frankenstein my own with a Pico, but I haven't gotten that far.
I searched for a schematic online, and came across the following
Schematic credit : https://www.researchgate.net/figure/Circuit-diagram-of-HC-SR04_fig2_334627562
Only one of the chips on my module are marked, the leftmost chip is an lm324. The center chip is presumable the mcu and the rightmost a max232.
Looking around the "max232" there isn't a single capacitor, not even a decoupling cap, let alone the charge pump caps.
Hmmm. What is it?
I pulled the chip off
Testing the chip out of circuit, I measure a zero ohm short between the input and output pins of the output driver (pins 10&7, 11&14)
No parasitic diodes from io pins to ground, resistance between vcc and ground measures open-circuit.
So far it looks like a pointless chip, just 2 jumper links in a 16-smd package.
I have nothing against simplifying or economizing a design, delete the max232 transceiver all together.
Don't put a bubble gum chip on the board.
Anything I should test before sanding the chip down to see what's inside?
