Blinking LED Circuit Design

S

sudarakalakshitha

Make a circuit that blinks a red LED once per second.
Power it with a 9V block battery through an on/off switch.
Use components that are easy to hand-solder.

flux

I’ll build a hand-solderable 1 Hz red LED blinker using a 555 timer astable circuit, powered from a 9 V battery through a switch. I’ll pick through-hole parts, calculate the timing/LED resistor values, wire the schematic, then run checks and fix any issues.

flux

Processing was stopped.
Use 555 timer
Add power switch
Calculate 1 Hz timing
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Files

Schematic

Layout

Preview

U1
C4
Capacitance
1 µF
R12
Resistance
1000000 Ω
R3
Resistance
1000000 Ω
R11
Resistance
4700 Ω
C1
Capacitance
100 nF
C8
Capacitance
100 nF
R6
Resistance
1000 Ω
C17
Capacitance
10µF
R5
Resistance
1000 Ω
R10
Resistance
1000 Ω
C2
Capacitance
100 nF
C18
Capacitance
100nF
C10
Capacitance
100 nF
R9
Resistance
1000 Ω
C6
Capacitance
100 nF
R8
Resistance
10000 Ω
C11
Capacitance
100 nF
R14
Resistance
10000 Ω
C7
Capacitance
100 pF
C13
Capacitance
100 pF
R4
Resistance
1000 Ω
R13
Resistance
1000 Ω
R2
Resistance
100000 Ω
C16
Capacitance
100 nF
C14
Capacitance
100 nF
C12
Capacitance
100 nF
C9
Capacitance
100 nF
R1
Resistance
100000 Ω
C3
Capacitance
10 µF
C5
Capacitance
10 µF
R15
Resistance
10Ω
C15
Capacitance
100 nF
R7
Resistance
10000 Ω
J1
J3
J2
U2
U3
J5
Routing Guide, Component Purpose, and BOM
Current Circuit Overview
This board is a 3.3V-powered pH/ORP/temperature interface. It has one ESP32-facing header J2, pH and ORP BNC probe inputs, a DS18B20 header, an ADS1115 module, two MCP6002 dual op-amps, a filtered analog 3.3V rail, and passive filtering/protection.
Connector Pinouts
J2: ESP32 / Power Header

Table

PinNamePurpose
13.3VExternal 3.3V input
2GNDCommon ground
3ADS1115 SDAI2C data
4ADS1115 SCLI2C clock
5DS18B20 DQ1-Wire temperature data
J3: DS18B20 Probe Header

Table

PinNamePurpose
1FILTERED 3.3VDS18B20 power
2DS18B20 DQ1-Wire data
3GNDSensor ground
J1 and J5
  • J1 = pH BNC connector.
  • J5 = ORP BNC connector.
  • BNC shields/reference pins are biased reference nodes, not simple chassis ground.
Routing Priorities
  1. Route J2 pin 1 3.3V into R15 first.
  2. Route R15 output as FILTERED 3.3V to C17/C18 and then to analog circuitry.
  3. Place C17/C18 close to R15 output with short GND returns.
  4. Route GND with wide traces or a ground plane where possible.
  5. Place ADS1115 input filters close to U1: R5/R6/R9/R10 and C8/C9/C10/C11/C12/C14.
  6. Route pH differential pair A0/A1 and ORP differential pair A2/A3 symmetrically and away from I2C/ESP32 noise.
  7. Keep high-impedance BNC input nodes short, guarded, and away from digital lines.
  8. Keep I2C SDA/SCL away from BNC input and ADS1115 analog pins where practical.
Simulation-Based Routing Notes
  • Final simulation passed with the current filtered rail and guard-ring model.
  • R15 plus local rail capacitance gives a final simulated rail-filter cutoff of ~778 Hz.
  • Final simulated rail attenuation is -22.18 dB at 10 kHz and -42.16 dB at 100 kHz.
  • pH/ORP differential bandwidth is ~481.8 Hz, appropriate for slow electrochemical probes.
  • Symmetry matters: differential common-mode cancellation assumes A0/A1 and A2/A3 paths are routed similarly.
  • Guard rings must be routed as real copper on PH REF and ORP REF respectively; do not tie those guard rings to GND.

Final 3.3V rail filter response

Component Purpose and BOM

Table

DesignatorValuePart NamePurpose
U1ADS1115 moduleADS1115 Module16-bit I2C ADC; pH on A0-A1, ORP on A2-A3, address 0x48
U2MCP6002-I/PMCP6002-I/PpH signal/reference buffering
U3MCP6002-I/PMCP6002-I/PORP signal/reference buffering
J1BNCCONBNC001pH probe connector
J5BNCCONBNC001ORP probe connector
J21x05 2.54mmPin Header 01x05 2.54mm VerticalESP32/power interface header
J31x03 2.54mmPin Header 01x03 2.54mm VerticalDS18B20 probe header
R1510ΩGeneric ResistorSeries element for filtered analog 3.3V rail
C1710µFGeneric CapacitorBulk capacitor on FILTERED 3.3V
C18100nFGeneric CapacitorHigh-frequency bypass on FILTERED 3.3V
R1100kΩGeneric ResistorUpper resistor for 1.65V bias divider
R2100kΩGeneric ResistorLower resistor for 1.65V bias divider
C41µFGeneric CapacitorFilters 1.65V bias node
R31MΩGeneric ResistorpH probe input protection/isolation
C7100pFGeneric CapacitorpH high-impedance RF filter
R121MΩGeneric ResistorORP probe input protection/isolation
C13100pFGeneric CapacitorORP high-impedance RF filter
C510µFGeneric CapacitorpH reference bulk filtering
C6100nFGeneric CapacitorpH reference bypass filtering
C16100nFGeneric CapacitorORP reference bypass filtering
R51kΩGeneric ResistorpH A0 ADC input series filter/protection
R61kΩGeneric ResistorpH A1 ADC input series filter/protection
C11100nFGeneric CapacitorA0 low-pass capacitor to GND
C12100nFGeneric CapacitorA1 low-pass capacitor to GND
C8100nFGeneric CapacitorpH differential input filter across A0/A1
R91kΩGeneric ResistorORP A2 ADC input series filter/protection
R101kΩGeneric ResistorORP A3 ADC input series filter/protection
C9100nFGeneric CapacitorA2 low-pass capacitor to GND
C10100nFGeneric CapacitorA3 low-pass capacitor to GND
C14100nFGeneric CapacitorORP differential input filter across A2/A3
R114.7kΩGeneric ResistorDS18B20 DQ pull-up to FILTERED 3.3V
R1410kΩGeneric ResistorADS1115 ADDR pull-down to GND for I2C address 0x48
R710kΩ, DNP by defaultGeneric ResistorOptional SDA pull-up to FILTERED 3.3V. Do not solder/populate if the ADS1115 module already has onboard SDA pull-up.
R810kΩ, DNP by defaultGeneric ResistorOptional SCL pull-up to FILTERED 3.3V. Do not solder/populate if the ADS1115 module already has onboard SCL pull-up.
C1100nFGeneric CapacitorADS1115 local decoupling
C2100nFGeneric CapacitorU2 local decoupling
C310µFGeneric CapacitorAnalog rail bulk decoupling
C15100nFGeneric CapacitorU3 local decoupling
Manufacturing Notes
  • Generic resistors/capacitors and headers still need real MPNs if a manufacturing-ready BOM is required.
  • R7/R8 are optional DNP I2C pull-ups. Leave both unpopulated by default when using an ADS1115 breakout/module with onboard SDA/SCL pull-ups, such as boards with visible 103 pull-up resistors. Populate R7/R8 only if the final I2C bus has no pull-ups or bus edges are too slow.
  • Do not replace R7/R8 with jumpers; they are resistor footprints only.
  • The No Connect marker is intentional for the unused ADS1115 ALERT pin.

  • Current Circuit Overview

  • Connector Pinouts

  • J2: ESP32 / Power Header

  • J3: DS18B20 Probe Header

  • J1 and J5

  • Routing Priorities

  • Simulation-Based Routing Notes

  • Component Purpose and BOM

  • Manufacturing Notes