Author Topic: What is the purpose of the IC in this SLR lightmeter circuit?  (Read 192 times)

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Offline julian1

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Schematic is the light-meter for a circa 1998/2000 slr camera. 

What is the function of the 10 pin IC within J100. Is it analog switch?, level adjust, switchable comparator?, analog sample-and-hold? Is it likely a custom part?

- SOUT (pin 5) connects to what appears to be a light dependent resistor.
- The analog signal is connected to the microcontroller ADC (AN0).
- SEL1, SEL2, SEL3 are uncertain select/switch functions driven by MCU gpio.
« Last Edit: March 03, 2020, 09:42:02 am by julian1 »

Offline Zero999

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Please post the complete circuit. It appears to be a sample and hold circuit.

Q1 is a FET, probably low power MOSFET, but I couldn't find a sane data sheet.

Offline julian1

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The complete analog section is shown.

I believe Q1 (pchannel fet connected to body/rail VDD) just allows the microcontroller to power on/off the analog section as a whole. Eg. by pulling AVDDCNT and the mosfet gate low to turn on.

Edit. I think there is some kind of integration/negative feedback with AOUT,AIN,SOUT around what looks like a light dependent resistor.
Edit 2. I now suspect the 10 pin IC is just level shifter - to bridge the digital voltage levels of the GPIO select pins to the analog circuit. eg. pull SOUT high - to get a LDR reading at the ADC.  pull the AOUT or AIN high to get reference voltage levels at the ADC.
« Last Edit: March 03, 2020, 09:52:35 am by julian1 »

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