Wichit Sirichote, wichit.sirichote@gmail.com
Replace the old VFD digital clock with a high efficiency LED display, a precision clock and more functions. Available now, 12 or 24 Time format.
The Nissan digital clock model 25820 with the Vacuum Fluorescent Display (VFD) consumes rather high power, approx. 1.4W. Heat produced inside the clock could cause malfunction and eventually the clock will stop functioning. People may fix it or replace it with an expensive genuine one.
The replacement clock provides 6 modes of operation.
This replacement kit is the new design using a high efficiency LED display, an accurate realtime clock, consuming less than 0.1W. The kit can replace the Nissan clock board with some modifications.
0 Normal clock display
1 Alternator charging voltage
2 Temperature sensor
3 Timer 0–9999 mins
4 Set temperature for radiator FAN control (50C to 95C)
5 Manual FAN control
RESET button will be mode selection. H and M buttons will be parameter settings for each mode..
Hardware
The clock is running by U4, DS1307 real-time chip with 32,768 Hz xtal.. The MCU is an 8051-based STC8G1K17, 16-pin microcontroller. The display is made of U2 and U3, the high brightness common anode 7-segment display 2281BS. The display driver is U1, TCM1637. U6, LM1117 is a +5V voltage regulator. The alternator voltage detection is measured with ADC channel 6. The temperature sensor is ADC channel 7. Optional FAN control with open collector output is P5.5 bit. J1 is an IAP loader. The software can be upgraded using STC programmer easily.
Component layout
The main components, MCU, RTC, and LED display are placed on the top layer of the board. The bottom layer is the TCM1637 display chip and the NTC sensor socket. The LED digit height is 0.28 inches. Latest software is available for 12 clock format. The last dot indicates AM/PM.
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Board Dimension
The board dimension is shown below. The unit is mils, 1/1000 inches. Multiply it with 0.0254 to convert to mm. The current version is designed for the digital clock model 25820 31U00, 0E000.
Wiring connection
Four pins at J2 are used to connect the clock board.
1. +B, always ON +12V battery (BLUE)
2. ACC, +12V when car power ON (WHITE)
3. DIM, +12V when low and high beam light ON (GREEN)
4. GND, 0V common ground (BLACK)
Mode of operation
Button RESET when pressed will increment MODE from 0 to 5.
Note
*with thermistor sensor, 2m cable long (used with mode 4)
**Long press M will reset the timer to 0000.
***Preset temperature, 75C for controlling the cooling fan. Adjusted by H and M button..
Example of Display on each MODE
Mode 0, normal clock running.
Mode 1, Alternator charging voltage, +14.0V
Mode 2, temperature display with NTC sensor.
Mode 3, Timer display in minute counting, 4 mins shown below. Maximum is 9999 mins. (approx. one week).
H button START, M button STOP and CLEAR (long press)
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Mode 4, Adjust the temperature for controlling the radiator fan. Preset on power up is 75C.
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Mode 5, Manual fan control, H button ON and M button OFF. Dot indicates FAN ON.
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Replacement steps (DIY)
1. Remove the clock from your car
2. Remove 4-pin cable with connector from the PCB
3. Solder the 4-pin connector to the new replacement kit.
4. Cut the plastic pin of each button, approx. 1.5mm. Place the clock board on the front panel, and test the button. It must be clicked when pressed.
5. Insert the temperature sensor cable.
7. Assemble the box with a snap lock.
12 Time Format
Available now in 12 time format. Right-hand dot indicates AM/PM, ON for PM and OFF for AM. The below photo shows the afternoon time between two boards.
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Connecting the external RELAY
The open collector NPN output is designed for connecting the external RELAY with opto-isolator input.
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Replacement Service
Replacement service is available worldwide. Ship your clock to Thailand. We will replace it, and test the new replacement and will ship it back to your home easily.
For different platforms on other cars, we can design a new board to fit your car also. Please contact me for more details.
Download
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More technical information, please contact Wichit Sirichote, wichit.sirichote@gmail.com
Last updated September, 2024
August 2024