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General => General Chat => Topic started by: julian1 on March 02, 2020, 08:43:00 pm

Title: What is the purpose of the IC in this SLR lightmeter circuit?
Post by: julian1 on March 02, 2020, 08:43:00 pm
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.
Title: Re: Understand circuit - J100 - analog switch? programmable gain amplifier?
Post by: Zero999 on March 02, 2020, 09:31:30 pm
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.
Title: Re: Understand circuit - J100 - analog switch? programmable gain amplifier?
Post by: julian1 on March 02, 2020, 10:30:22 pm
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.