Ultrasonic module reverse engineering

Projects / Project Swiftlet  "Ultrasonic Module - Let's get physical" Original post date: 06/27/2015

This is a physical teardown of the HC-SR04 Ultrasonic Range Finder modules sold from China. This part is the old fashion kind. This is just for completeness.

Observations:

• No copyright, no designers name or anything.
• Some board uses the old LM324 and some uses the SGM324 (CMOS RRIO).
• One of the boards with the SGM324 has the opamp pin 5 grounded in the PCB layout, but everything else looks identical. After modding it to match the rest of the boards, it works better.
• Rest of the parts have part# removed.
• U3 seems different
• Not much change except for a few cost reduction and part designation renumbering
• Judging from what's been selling on the ebay/Chinese sites, the most likely part# that is on the module is: TCT40-16R/T-2 from Sunway / Shenghui

Components is placed on a printout of the scan

1. Take a picture, print it out and strip parts off the PCB one at a time. The parts are taped down to keep track of what goes where on the board. Make sure that it is in a geographical stable location away from wind, pets etc. :) Some people like to use icecube trays for these type of work.
2. Scan the board in a flat bed scanner
3. Import the scan into an image manipulation package
4. Scan pan rotate zoom enhance!

Bottom scan:

Select the silkscreen areas and re-level to reveal what's under.

Readjust the tint to match the rest of the board. (by eyeball)

(I am skipping clean and repair image as it will take me an hour or so)

Flip the scan horizontally for merging (click for high res. image)

Top Scan: minor de-noise applied (click for full image)

I'll let someone merge the image. The board is simple enough for me to skip that step.

5. Measure component values, sketch out the schematic

I saw a variant of R2 = 56K (563) in some of my modules. All it means is that the gain will be lower.

Original schematic from Emil's Projects: "Making a better HC-SR04 Echo Locator". Updated by me to the most recent PCB version.

Annotated schematic for the differences - Click to see full resolution