Blinking LED Circuit Design
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.
Thought
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.
Worked for 42 sec
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Project Specification
Project
ESP32-C3 ADS1115 pH/ORP Sensor Interface
Current Design Scope
This project is a 3.3V-powered analog front-end for measuring pH, ORP, and temperature with an external ESP32-class controller. The board does not include batteries, TP4056 charging, debug headers, or an onboard ESP32. The ESP32 connection is through one 5-pin header carrying power and digital signals.
External Interface: J2
Use these names for firmware and wiring documentation:
Table
| J2 Pin | Name | Direction | Purpose |
|---|---|---|---|
| 1 | 3.3V | Input | External 3.3V supply from ESP32 board or regulated source |
| 2 | GND | Common | Common ground with ESP32 and probes |
| 3 | ADS1115 SDA | Bidirectional | I2C data to ADS1115 module |
| 4 | ADS1115 SCL | Input to ADS1115 | I2C clock from ESP32 |
| 5 | DS18B20 DQ | Bidirectional | 1-Wire data for DS18B20 temperature probe |
ADS1115 ADDR is fixed locally to GND through R14 = 10kΩ for default address 0x48. ADS1115 ALERT is intentionally unused/no-connect.
Power Architecture
External 3.3V enters at J2 pin 1 and feeds the filtered analog rail through R15.
Text
J2 pin 1 3.3V -> R15 10Ω -> FILTERED 3.3V FILTERED 3.3V -> C17 10µF to GND FILTERED 3.3V -> C18 100nF to GND
The FILTERED 3.3V rail powers U1 ADS1115 module, U2/U3 MCP6002 op-amps, J3 DS18B20 sensor power, pull-ups, and the analog bias/reference networks.
Sensor Architecture
- J1 is the pH BNC input connector.
- J5 is the ORP BNC input connector.
- J3 is the DS18B20 temperature sensor header.
- U1 ADS1115 module digitizes pH and ORP in differential mode.
- U2 MCP6002 buffers the pH signal/reference paths.
- U3 MCP6002 buffers the ORP signal/reference paths.
ADC Channel Map
Table
| Measurement | ADS1115 Mode | Positive Input | Negative Input | Functional Net |
|---|---|---|---|---|
| pH | Differential | A0 | A1 | ADS1115 PH A0 - ADS1115 PH A1 |
| ORP | Differential | A2 | A3 | ADS1115 ORP A2 - ADS1115 ORP A3 |
Firmware must read pH as A0-A1 and ORP as A2-A3. Do not use single-ended readings for the final measurement because the analog design relies on differential cancellation of the mid-supply reference.
Key Component Values
- R15 = 10Ω analog supply filter resistor
- C17 = 10µF analog rail bulk capacitor
- C18 = 100nF analog rail bypass capacitor
- R1/R2 = 100kΩ / 100kΩ mid-supply bias divider
- C4 = 1µF bias filter
- R3/R12 = 1MΩ pH/ORP probe input protection resistors
- C7/C13 = 100pF high-impedance input RF filters
- R5/R6/R9/R10 = 1kΩ ADS1115 input series filters/protection
- C8/C14 = 100nF differential ADC input filters
- C9/C10/C11/C12 = 100nF ADC input-to-GND filters
- R11 = 4.7kΩ DS18B20 DQ pull-up
- R14 = 10kΩ ADS1115 ADDR pull-down
- R7/R8 = 10kΩ optional/DNP I2C pull-ups to FILTERED 3.3V. Leave unpopulated by default if the ADS1115 module already has onboard SDA/SCL pull-ups; populate only if no other I2C pull-ups are present.
Simulation Summary
Final simulation of the updated circuit with R15/C17/C18, local decoupling, and PH/ORP guard-ring modeling gives:
Table
| Result | Value |
|---|---|
| Overall functional result | PASS |
| FILTERED 3.3V rail cutoff | ~778 Hz |
| Rail attenuation at 100 Hz | -0.0716 dB |
| Rail attenuation at 1 kHz | -4.221 dB |
| Rail attenuation at 10 kHz | -22.18 dB |
| Rail attenuation at 100 kHz | -42.16 dB |
| pH/ORP differential bandwidth | ~481.8 Hz |
| pH ADC range for ±414 mV probe input | A0 ≈ 1.236V to 2.064V, A1 ≈ 1.650V |
| ORP ADC range for ±1.0V probe input | A2 ≈ 0.650V to 2.650V, A3 ≈ 1.650V |
| Guard-ring verification | PH guard tied to PH REF; ORP guard tied to ORP REF; neither tied to GND |
Simulation plots:
Image
Image
Image
Firmware Requirements
- Configure ADS1115 at address 0x48.
- Treat R7/R8 as optional DNP hardware pull-ups: do not solder them if the ADS1115 module or ESP32 side already provides I2C pull-ups.
- Use differential reads: A0-A1 for pH, A2-A3 for ORP.
- Use lower ADS1115 data rates and averaging/median filtering for stable readings.
- Read DS18B20 on J2 pin 5 / J3 pin 2 using 1-Wire.
- Calibrate pH offset at pH 7 and slope using buffer solutions.
- Temperature compensate pH slope using DS18B20 reading.
Current Validation Status
ERC reports no open errors or warnings. PCB routing is still expected to require DRC/airwire cleanup after layout routing.
Project
Current Design Scope
External Interface: J2
Power Architecture
Sensor Architecture
ADC Channel Map
Key Component Values
Simulation Summary
Firmware Requirements
Current Validation Status
