I love watching Limor/Lady Ada take apart a Consumer Electronic device and explain to us what the chips are and what is going on. I thought what a great learning opportunity to take something that I have some familiarity with – in this case pH and EC circuits – and find a product to take apart and figure out how the circuit works.
The product I picked was the ph/EC-983. I picked up a couple on eBay.
This handy tool integrates a pH and EC probe as well as gives a temperature reading. It is inexpensive and if it is “good enough” I was thinking it would be super amazing to plunk the probe in the nutrient bath. I would use firmware to take pH/EC measurements and use the measurements to adjust the pH and nutrients.
I was mostly interested in the bottom piece. The bottom piece contains the pH and EC probes:
I was thinking if I could figure out the signals coming out of the probe:
So that I could put the probe in the nutrient bath and connect up a pH/EC circuit to be monitored through firmware.
Hmmm…I couldn’t pry apart the device in the nice, clean way Lady Ada is able to…so…out came the Dremel!
The Active Parts
To get started, I looked at the active parts.
These two images show the location of the parts:
Two of the chips are the HEF 4053BT (data sheet):
From the data sheet: The HEF4053B is a triple single-pole double-throw (SPDT) analog switch, suitable for use as an analog or digital multiplexer/demultiplexer. This page on Basic Electricity has a great discussion on switches including SPDT switches.
Another is the HEF 4011BT (data sheet):
From the data sheet: The HEF4011B is a quad 2-input NAND gate.
Another chip is a variant on the 062C dual op amp (data sheet):
The internal ICL7106 (data sheet):
From the data sheet: TheICL7106 is designed to interface with a liquid crystal display(LCD)…
Unfortunately, I got a little too aggressive with the Dremel. I’m still able to make out this chip is a HEF4030BT (data sheet):
From the data sheet: The HEF4030B is a quad 2-input EXCLUSIVE-OR gate.
Drat…the Dremel scratched the markings off this chip. I can tell it is a Maxim and there looks to be A1601…or A1801…or…:
The SGM3005 XMS (data sheet):
From the data sheet: The SGM3005 is a dual, low on-resistance, low voltage, bidirectional, single-pole/double-throw (SPDT) CMOS analog switch designed to operate from a single 1.8V to 5.5V power supply.
At this point, my eyes hurt. Time to stop for now.