1. Introduction
This document provides detailed instructions for assembling, setting up, and operating the ICL7107 5V DC Digital Voltmeter DIY Electronic Kit. Designed for DIY enthusiasts, this kit allows you to build a high-precision digital voltmeter with a clear red display. Please read all instructions carefully before beginning assembly.
2. Product Features
- Fast reaction speed and high precision.
- Clear, intuitive reading with good stability.
- Advanced and reasonable circuit design with strong anti-interference ability, effectively suppressing high-frequency interference.
- Constructed from good quality materials with excellent technology, ensuring beautiful appearance, long service life, and easy installation.
- Suitable for welding and assembling by DIY enthusiasts.
3. Technical Specifications
| Parameter | Value |
|---|---|
| Working Voltage | DC 5V |
| Working Current | 35mA |
| Measurement Accuracy | Calibratable for high precision |
| Measuring Range (3 levels) | 0-2V, 0-20V, 0-200V |
| PCB Size | 70.6mm x 39mm |
| Meter Head Mounting Hole Size | 77mm x 40mm |
| Display Window Size | 51mm x 24mm |
| Display Color | Red |
| Type | Voltage Regulator |
| Application | Computer |
| Package | SOP |
| Condition | New |
4. Kit Contents
The DIY kit includes the following components:
- 1x PCB board
- 3x 1N4148 diodes
- 1x 5.1V voltage regulator diode
- 1x 100 ohm resistor
- 1x 270 ohm resistor
- 2x 2K resistors
- 1x 20K resistor
- 1x 47K resistor
- 1x 56K resistor
- 2x 100K resistors
- 1x 1M resistor
- 1x 2.2MH inductance
- 2x 104 monolithic capacitors
- 2x 101 monolithic capacitors
- 1x 224 monolithic capacitor
- 1x 474 monolithic capacitor
- 2x 10UF25V electrolytic capacitors
- 1x C1815 transistor
- 1x TL431 voltage reference
- 2x 3296-202 Potentiometers
- 1x XH2.54-2P upright seat
- 1x XH2.54-2P line
- 1x KF301-2-seat terminal block
- 1x 40P chip holder (IC socket)
- 1x ICL7107 Chip
- 4x 0.56 inch one digit digital tubes (7-segment displays)
- 1x Case
- 4x M2*6 self-tapping screws
5. Assembly Instructions
Tools required (not included): Multimeter, electric soldering iron, water pliers.
Follow these steps to assemble your voltmeter kit:
- Component Identification: Familiarize yourself with all the components provided in the kit. Refer to the component layout diagrams for placement.
Figure 3: PCB Component Layout 
Figure 4: Resistor Placement Guide 
Figure 5: Diode Placement Guide - Solder Smaller Components First: Begin by soldering the smallest components to the PCB, such as resistors and diodes, followed by capacitors, transistors, and potentiometers.
- Install IC Socket: Solder the 40P chip holder (IC socket) onto the PCB. Ensure correct orientation.
- Install Digital Displays: Solder the four 0.56 inch one-digit digital tubes (7-segment displays) onto the designated positions on the PCB.
- Insert ICL7107 Chip: Carefully insert the ICL7107 chip into its socket. Pay close attention to the direction of the chip's U port (notch or dot) and ensure it matches the orientation marked on the PCB socket. Do not insert the chip backwards to avoid damage.
Figure 6: ICL7107 Chip Insertion Direction - Mount PCB in Case: Secure the assembled PCB into the provided case using the M2*6 self-tapping screws.
Figure 7: Internal Screw Locations for Case Mounting - Review Circuit Diagram: For a comprehensive understanding of the connections, refer to the circuit diagram.
Figure 8: ICL7107 Voltmeter Circuit Diagram
6. Setup and Calibration
- Power Connection: Connect a DC 5V power supply to the designated positive and negative terminals on the board.
- Measurement Connection: Connect the voltage to be measured to the 'Measure' input terminals (positive and negative).
- Calibration: To achieve high precision, the voltmeter can be calibrated. Input a known, stable voltage (e.g., from a calibrated power supply). Then, adjust the calibration potentiometer until the value displayed by the voltmeter matches the measurement value from a reference multimeter. Specifically, adjust the potentiometer so that the voltage between pin 36 and pin 35 of the ICL7107 chip is 100mV.
Figure 9: Power, Measurement, and Calibration Points
7. Operating Instructions
Once assembled and calibrated, connect the voltmeter to the circuit where you wish to measure voltage. The red digital display will show the measured voltage. If the measured voltage exceeds the selected range, the display will show '1' or '-1' as an overrange indicator.
8. Measurement Range Selection
The voltmeter supports three measurement ranges, selected by soldering specific points on the PCB and choosing the appropriate RX welding resistance value:
- 0-2V Range: Weld the two solder points labeled '0-2V' together. The RX welding resistance value should be 1K. This range is for measuring small voltages.
- 0-20V Range: Weld the two solder points labeled '0-20V' together. The RX welding resistance value should be 100K. This range is for measuring low and medium voltages.
- 0-200V Range: Weld the two solder points labeled '0-200V' together. The RX welding resistance value should be 1M. This range is for high voltage measurement.
The kit includes 100K and 1M resistors for RX, allowing you to select the appropriate range for your application.
9. Ammeter Conversion
This voltmeter can also be converted into an ammeter (0-2A range). To do this:
- Reserve a 2W 0.1Ω high-precision resistance welding position on the board.
- Weld the appropriate resistance into this position.
- The RX resistor does not need to be welded for ammeter functionality.
10. Troubleshooting
- No Display: Check power supply connections (DC 5V) and ensure the ICL7107 chip is inserted correctly and fully seated in its socket. Verify all soldered connections for continuity.
- Incorrect Readings: Perform calibration as described in Section 6. Ensure the correct measurement range is selected (Section 8) and the RX resistor is properly installed for the chosen range.
- Overrange Display ('1' or '-1'): The measured voltage exceeds the currently selected range. Switch to a higher measurement range if applicable.
- Flickering Display: Ensure stable power supply and check for any loose connections or cold solder joints.
11. Maintenance
- Keep the voltmeter clean and dry.
- Avoid exposing the device to extreme temperatures or humidity.
- Do not attempt to repair complex internal issues unless you are a qualified technician.
12. Warranty and Support
This DIY kit is intended for educational and hobbyist use. Due to the nature of DIY assembly, specific warranties may vary. For technical support or inquiries, please contact the seller directly.
13. Additional Resources
A detailed user manual in PDF format is available for further reference. You can access it here: ICL7107 Voltmeter User Manual (PDF)
