24 September 2023

Prescaler output to VO pin (HLK-LD1115H)

Now that the prescaler has been enabled in the Hi-Sense HLK-LD1115H 24 GHz radar module, I would like to have that signal easily accessible.

Let's dive into another hardware mod.

As already observed, the DIVOUT signal goes to pin 12 of the microprocessor. Additionally there is a 100 ohm resistor in series, close to the uP. The firmware on the microprocessor seems to ignore this new input, so the 100 ohm resistor is a good point to intercept the prescaler output.

Next to it there's another 100 ohm resistor (a tiny black rectangle), that protects the VO movement/presence detection signal coming out of pin 11 of the microprocessor (tnx Mauro for the info!). Cool, VO goes all the way to the pin header!

Here is the plan: remove both 100 ohm resistors and create a jumper as shown in the picture below. If you are brave enough you can use a 100 ohm resistor, like rotating 90 degrees one of the originals. Click on the picture to get a larger version and see the small details.

(Not reversible) Mod to bring DIVOUT to VO pin.

Guess what? It works. Now it's easier to see frequency drift with temperature and experiment with thermal insulation.

Next step will be to disable the transmission in one module so that it becomes "receive only" (act on TXON signal) and try to receive the other module. This might require also some action on the frequency control voltage.

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