1. Introduction
The PLJ-8LED-H is a cost-effective frequency display component featuring an 8-bit digital tube display. It is primarily designed for displaying frequency values in transceivers and other electronic equipment, and can also be utilized for general frequency measurement tasks. This module is characterized by its compact and delicate design, reliable performance, clear visual effect, and economical cost.
Figure 1: Front view of the PLJ-8LED-H module with the display showing '29.600.000'. This image highlights the dual frequency design and preset modes.
2. Safety Information
- Ensure the power supply voltage is within the specified range (DC 9V ~ 15V) to prevent damage.
- Observe correct polarity when connecting the DC power input. The module includes reverse polarity protection, but proper connection is always recommended.
- Avoid touching the circuit board components while the module is powered on.
- Do not expose the module to moisture, extreme temperatures, or corrosive environments.
- Handle with care to prevent physical damage to the display or circuit board.
3. Product Overview and Features
The PLJ-8LED-H module incorporates advanced design for precise frequency measurement and display.
Key Features:
- Microchip PIC16F648A: Utilizes a 2.4 GHz frequency meter based on the PIC16F648A microcontroller.
- Temperature-Compensated Crystal Oscillator: Employs a 2.5 ppm VC-TCXO (Voltage Controlled Temperature-Compensated Crystal Oscillator) for enhanced accuracy.
- Precise Time Algorithm: Features unique gate control and a precise non-timed interrupt algorithm.
- Adjustable Gate Time: Offers gate (display refresh) times of 0.01 seconds, 0.1 seconds, and 1.0 seconds for real-time frequency display.
- Three-Channel Measurement: Supports single-ended input design with three frequency measurement channels: Low Channel, High Channel, and Auto Channel.
- Dual Frequency Design: Allows separate presetting of value and IF (Intermediate Frequency) / down modes.
- High Brightness Digital Display: Equipped with eight 0.56-inch high-brightness digital LED displays.
- Adjustable Brightness: Eight levels of adjustable display brightness.
- Simple Operation: Features a simple and reasonable circuit structure with two-button control.
- Automatic Settings Save: Automatically saves settings, which are recalled directly upon boot-up.
Figure 2: Angled view of the PLJ-8LED-H module, emphasizing its simple circuit structure and two-button control.
4. Specifications
| Feature | Description |
|---|---|
| Model | PLJ-8LED-H |
| Display Type | 8-bit 0.56-inch Digital LED (Red or Blue font options) |
| Gate Time (Display Refresh) | 0.01 S / 0.10 S / 1.0 S |
| Measurement Channels | Low Channel, High Channel, Auto Channel (low impedance) |
| Low Channel Measuring Range | 0.1 MHz ~ 60 MHz |
| Low Channel Accuracy | ± 100Hz (0.01s gate), ± 10Hz (0.1s gate), ± 1Hz (1.0s gate) |
| Low Channel Sensitivity | 0.1-10 MHz: >60mVPP; 10-60 MHz: >60mVPP |
| High Channel Measuring Range | 20 MHz ~ 2.4 GHz (divided by 64) |
| High Channel Accuracy | ± 6400Hz (0.01s gate), ± 640Hz (0.1s gate), ± 64Hz (1.0s gate) |
| High Channel Sensitivity | 20-30 MHz: >100mVPP; 30-60 MHz: >50mVPP |
| IF Settings | Independent double-IF design, 100 Hz min step, 0 ~ 99.9999 MHz range, increase/decrease mode |
| Frequency Reference | 5032 package 13.000MHz VC-TCXO, ± 2.5 ppm stability |
| Operating Voltage | DC 9V ~ 15V (with reverse polarity protection) |
| Current Consumption | Max 160 mA (DC12V, red LED, max brightness) |
| Display Digits | Highest display eight digits |
| Brightness Adjustment | Eight adjustable levels (factory set to maximum) |
| Physical Dimensions (LxWxH) | 125.5 mm x 25.5 mm x 21.5 mm |
| Net Weight | Approx. 46 g |
| Onboard Interfaces | DC IN (HX2.54-2P socket), RF IN (HX2.54-2P socket), ICSP (2.54-6P Pin) |
Figure 3: Bottom view of the PLJ-8LED-H PCB, revealing the electronic components and layout.
5. Setup
5.1 Package Contents
Before proceeding, ensure all components are present:
- 1 x PLJ-8LED-H Frequency Counter Module
- 2 x Connecting Cables (for power and signal input)
Figure 4: The PLJ-8LED-H module packaged with two connecting cables.
5.2 Power Connection
- Locate the DC IN (Power Interface) on the module, which is an HX2.54-2P socket.
- Connect one of the provided cables to the DC IN socket.
- Connect the other end of this cable to a stable DC power source providing 9V to 15V. Ensure correct polarity.
5.3 Signal Input Connection
- Identify the RF IN (signal input) on the module, also an HX2.54-2P socket.
- Connect the second provided cable to the RF IN socket.
- Connect the other end of this cable to the signal source whose frequency you wish to measure.
6. Operating Instructions
The module features two buttons for control and configuration.
6.1 Gate Time Selection
The gate time determines how frequently the display refreshes and impacts measurement accuracy. Shorter gate times provide faster updates but lower accuracy, while longer gate times offer higher accuracy with slower updates.
- Available gate times: 0.01 seconds, 0.1 seconds, 1.0 seconds.
- Refer to the specifications for accuracy corresponding to each gate time.
6.2 Measurement Channel Selection
The module supports three measurement channels:
- Low Channel: For frequencies between 0.1 MHz and 60 MHz.
- High Channel: For frequencies between 20 MHz and 2.4 GHz. This channel divides the input frequency by 64.
- Auto Channel: Automatically selects between the low and high channels based on the input signal frequency, with a threshold of 60 MHz. If the input signal amplitude is insufficient for the Auto Channel to correctly identify frequencies above 60 MHz, manual selection of the High Channel may be necessary.
6.3 IF Settings
The module features an independent double-IF design, allowing for adjustment of intermediate frequencies.
- The minimum frequency step for adjustment is 100 Hz.
- The frequency range for IF settings is 0 ~ 99.9999 MHz.
- You can set the IF frequency mode to either increase or decrease.
6.4 Display Brightness Adjustment
The 8-bit LED display's brightness can be adjusted through eight levels. The factory default is set to maximum brightness.
6.5 Saving Settings
All configured settings are automatically saved and will be loaded directly when the module is powered on again.
Figure 5: Side view of the PLJ-8LED-H module, showing the display, control buttons, and mounting holes.
7. User Tips
- Measuring FM Broadcast Frequencies (88-108 MHz): Yes, the PLJ-8LED-H module can measure frequencies within the FM broadcast band (88 to 108 MHz). For these frequencies, you should use the 'High Channel' setting, as the 'Auto Channel' typically switches to the high range above 60 MHz, but manual selection ensures optimal performance for signals in this range. The High Channel supports measurements up to 2.4 GHz.
- Optimizing Accuracy: For the most accurate readings, especially for stable signals, select the 1.0-second gate time. For faster, less critical measurements, use the 0.01-second or 0.1-second gate times.
- Signal Strength: If you encounter unstable readings, ensure your input signal has sufficient amplitude. Refer to the sensitivity specifications for each channel.
8. Troubleshooting
- No Display/Module Not Powering On:
- Check power supply voltage (DC 9V-15V).
- Verify power cable connections and polarity.
- Inaccurate or Unstable Readings:
- Ensure the correct measurement channel (Low, High, Auto) is selected for the frequency range.
- Increase the gate time (e.g., to 1.0 seconds) for higher accuracy.
- Check the input signal strength and quality. Weak or noisy signals can lead to unstable readings.
- Verify signal input cable connections.
- Display Too Dim/Bright:
- Adjust the display brightness using the control buttons.
- Module Not Responding to Buttons:
- Power cycle the module (turn off and on).
- Ensure buttons are not physically stuck.
9. Maintenance
- Cleaning: Use a soft, dry cloth to clean the module. Do not use liquid cleaners or solvents.
- Storage: Store the module in a dry, dust-free environment when not in use.
- Component Inspection: Periodically inspect the circuit board for any signs of damage, loose connections, or overheating components.
- Firmware: The ICSP interface is for programming. Firmware updates are typically not user-serviceable and should only be performed by qualified personnel if necessary.
10. Warranty and Support
For warranty information and technical support, please contact your retailer or the manufacturer directly. Keep your purchase receipt as proof of purchase.
