Sharp 1801v Calculator

This calculator helps determine the correct resistor value for a Sharp 1801V calculator's contrast adjustment.

Understanding the Sharp 1801V Contrast Adjustment

The Sharp 1801V is a fascinating microcontroller from the 1980s, known for its use in early calculators and other embedded systems. A crucial aspect of its operation, especially for devices with LCD displays, is the contrast adjustment. This adjustment is typically achieved using a variable resistor (potentiometer) or a fixed resistor in conjunction with the microcontroller's internal circuitry.

The Sharp 1801V likely uses a circuit that relies on a voltage divider to set the LCD bias voltage, which directly affects the contrast. The goal is to find an appropriate resistor value that allows the display to be legible under various conditions, while not exceeding the microcontroller's operational parameters.

The Calculation Explained

The calculator above estimates the required resistance (R) for the contrast adjustment circuit based on typical parameters associated with such devices. While specific schematics for every application of the 1801V might vary, the following formula represents a common approach for voltage divider-based contrast control:

The fundamental principle involves ensuring that the voltage division provides the correct bias for the LCD. A common configuration involves setting up a voltage divider where the desired contrast voltage (V_contrast) is achieved.

The calculator uses a formula derived from basic circuit analysis, aiming to find the resistance needed to achieve a specific voltage at the LCD driver input, considering the supply voltage (Vcc), a reference voltage (Vfl), and an offset voltage (Voffset).

The formula implemented is:

R = (Vcc - Vfl - Voffset) / (Iop / 1000) - PresetResistor

Where:

• R is the calculated resistance in Ohms.
• Vcc is the supply voltage of the microcontroller (in Volts).
• Vfl is a reference voltage, often related to the "flicker" voltage that helps define the LCD's operational range (in Volts).
• Voffset is an offset voltage that might be present in the circuit (in Volts).
• Iop is the operating current of the circuit, typically measured in milliamperes (mA). We convert this to Amperes by dividing by 1000.
• PresetResistor is the value of any fixed resistor already in the circuit or a baseline value to adjust from.

How to Use the Calculator

1. Vcc (Supply Voltage): Enter the operating voltage of your Sharp 1801V circuit. Common values are 3V, 5V, or 9V, depending on the device.
2. Vfl (Flicker Voltage): Input the typical flicker voltage specified for the LCD or the circuit design. This can sometimes be approximated if not precisely known.
3. Voffset (Offset Voltage): Enter any known DC offset voltage in the contrast control path.
4. Iop (Operating Current): Enter the expected operating current for the contrast adjustment circuit, usually in milliamperes (mA).
5. Preset Resistor: If your circuit includes a fixed resistor as part of the contrast adjustment (e.g., a fixed resistor in series with a potentiometer), enter its value here. If you are calculating a single fixed resistor, you can set this to 0.

Clicking "Calculate Resistor" will provide the estimated resistance needed for your Sharp 1801V application. This value can then be used to select an appropriate fixed resistor or set a potentiometer.

Important Considerations

• Approximation: This calculation is based on common circuit principles. The actual optimal value may vary depending on the specific LCD panel, the exact circuit design, and environmental factors.
• Testing: Always test the calculated resistor value in your actual circuit. You may need to fine-tune the resistance (e.g., by using a potentiometer or trying nearby standard resistor values) to achieve the best contrast.
• Component Datasheets: Refer to the datasheets for the Sharp 1801V microcontroller and the specific LCD panel you are using for precise voltage and current requirements.
• Safety: Ensure you are working with appropriate voltages and take necessary safety precautions when dealing with electronic circuits.