Explorer

The sensor circuit and how it connects, at schematic level. The parts a bug touched light up.

Fig. 1 · sensor circuitUSB connectorLM317 regulatorRSET 240 ΩNTC thermistorRADJ 392 ΩRFIX 10kCOUT 10 µFRPWR 1kTP1 test pointRRST 10kOp-amp bufferPower LEDCRST 100 nFRAA 1.59kCAA 100 nFReset buttonMicrocontrollerMCURLED 220 ΩStatus LEDRSDA 4.7kRSCL 4.7kI²C headerUSB 5 VLM317 → 3.3 VNTC sensorop-amp buffer1 kHz filterresetpower LEDstatus LEDI²C

Parts laid out in schematic order and wired as the netlist connects them: blue is the 3.3 V rail, violet 5 V, orange the sensor signal. Not a PCB layout. Hover a part.

VUSBCINVREFEREGRSETRADJCOUTRPWRDPWRRNTCRFIXVTP1EBUFRAACAARRSTCRSTRBTNVGPIORLEDDLEDRSDARSCLGNDadcadjainbufgpiopledrefrstsclsdasensesledusbv33

Coloured dots are parts, small dots are nets (wires). This is what a schematic is: parts joined by nets.

PartBlockNetsValueNote
VUSBPowerusb – 0DC 5
CINPowerusb – 010uinput bulk capacitor
VREFPowerref – adjDC 1.25regulator reference: REF sits 1.25 V above ADJ (no current flows in ADJ)
EREGPowerv33 – 0 – ref – v331megregulator output stage drives OUT (v33) to REF, as an LM317 does
RSETPowerv33 – adj240output = 1.25 V * (1 + RADJ / RSET) = 3.3 V
RADJPoweradj – 0392
COUTPowerv33 – 010uoutput capacitor
RPWRPower-on LEDv33 – pled1k
DPWRPower-on LEDpled – 0VF=2.1
RNTCTemperature sensorv33 – sense10k
RFIXTemperature sensorsense – 010k
VTP1Temperature sensorain – senseAC 1TP1 test point: 0 V at DC, injects 1 V AC for the filter check
EBUFTemperature sensorbuf – 0 – ain – buf1megop-amp voltage follower, so the ADC does not load the divider
RAATemperature sensorbuf – adc1.59kRC anti-aliasing filter, cutoff 1 kHz, into the MCU ADC pin
CAATemperature sensoradc – 0100n
RRSTResetv33 – rst10k
CRSTResetrst – 0100n
RBTNResetrst – 01greset button: 1g released, 1m pressed
VGPIOStatus LEDgpio – 0DC 3.3
RLEDStatus LEDgpio – sled220
DLEDStatus LEDsled – 0VF=2.0
RSDAI2C bus pull-upsv33 – sda4.7k
RSCLI2C bus pull-upsv33 – scl4.7k