Ohm's Law
Calculate voltage, current, resistance and power from any two known values.
Open calculatorAndroid + web engineering toolkit
Engineering tools for the field.
Practical electronics calculations, engineering references and protocol utilities for technicians, installers, engineers, students and makers. Calculator values remain in your browser and are not submitted to GSDev.
No accountNo analyticsNo calculation uploads
Functional engineering tools
Six useful tools in the first batch. All calculations execute client-side.
LED Resistor
Calculate series resistance and estimated resistor power dissipation.
Open calculatorVoltage Divider
Calculate unloaded divider output voltage and divider current.
Open calculatorVoltage Drop
Estimate copper conductor voltage drop for DC/single-phase and three-phase circuits.
Open calculatorUnit Converter
Convert electrical, dimensional and temperature engineering units.
Open converterResistor Colour Code
Decode a standard four-band resistor value and tolerance.
Open decoderOhm's Law calculator
Enter any two known values and leave the others blank.
LED series resistor calculator
For simple DC series LED circuits.
Voltage divider calculator
R1 from Vin to Vout and R2 from Vout to ground.
Cable voltage-drop estimator
Copper conductor estimate for preliminary engineering use.
Engineering unit converter
Common electrical and physical units.
Four-band resistor colour code
Select each band from left to right.
RS485 & Modbus reference
The public website provides safe reference material. Direct serial-device access is reserved for the Android app and compatible hardware.
Example Modbus RTU request
> Slave: 1
> Function: 03 - Read Holding Registers
> Start: 0000
> Quantity: 0002
TX 01 03 00 00 00 02 C4 0B
RX 01 03 04 00 64 00 32 ...
RS485 quick reference
| Item | Typical practice |
|---|---|
| Topology | Daisy-chain / bus; avoid star wiring |
| Termination | Typically 120 Ω at both physical ends |
| Polarity | A/B naming varies by manufacturer |
| Reference | A common signal reference may be required |
Common Modbus functions
| Code | Function |
|---|---|
| 01 | Read Coils |
| 02 | Read Discrete Inputs |
| 03 | Read Holding Registers |
| 04 | Read Input Registers |
| 05 | Write Single Coil |
| 06 | Write Single Register |
| 15 | Write Multiple Coils |
| 16 | Write Multiple Registers |
Follow the connected equipment manufacturer's wiring instructions and confirm electrical compatibility before connecting hardware.
One GSDev Engineering Tools platform
The website and Android app share the same visual identity and tool set. The Android app can later add hardware-specific capabilities while the website remains a secure browser-based calculator and reference resource.
Calculator results are engineering aids and do not replace datasheets, applicable standards, professional design verification or site-specific safety requirements.