cellularmitosis/README.md

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Arduino LCD display for HP 34401A

Here is an Arduino sketch which reads values
from an HP 34401A
over a serial connection and displays them on an LCD screen.
See also the eevblog thread.


Buy why tho?

Whereas the 34401A only displays 6 digits via its front-panel display, it makes a 7th digit available via the serial port.
This sketch makes that 7th digit visible via the LCD display.
RS232 to TTL board

This project uses an RS232-to-TTL adapter, specifically this one from eBay:


The HP 34401A requires that the DSR pin be enabled before it will transmit data.
To do this, solder a pull-up resistor (e.g. 10k) from VCC to DB9 pin 6:


Caveats

This sketch is too slow to handle some of the faster sample rates (e.g. "fast 4-digit" mode) of the 34401A.
However, the whole point of using this sketch is to get access to the 7th digit, so you'd likely be using fast or slow 6-digit mode, which this sketch handles correctly.
Formatting tests:


## hp34401a-lcd.ino
// hp34401a-lcd.ino: Arduino sketch to display HP 34401A readings on a 16x2 LCD
// as well as send them out the serial port.

// Copyright 2022 Jason Pepas.
// Released under the terms of the MIT License.
// See https://opensource.org/licenses/MIT.

// Setup:

// First, set your 34401A to "talk only" mode:
// Menu -> I/O Menu -> HP-IB Addr -> 31.

// Next, prepare a RS232-to-TTL adapter by soldering a pull-up resistor from
// the DB9 pin 6 (the DSR pin) to VCC (5V).
// See https://gist.github.com/cellularmitosis/1582236f226e9d98075a0c971eb4168c for soldering details.

// Thanks to:
// https://www.eevblog.com/forum/testgear/external-display-for-agilent-34401a-(or-any-dmm-with-rs232-output-stream)/msg326470/#msg326470
// "Set DB9 pin 6 DSR high 5V"


// Pins:

#define LED_pin (13)  // The onboard Arduino LED.

// The RS232-to-TTL adapter will have four pins:
//  Pin 1: GND, connect to Arduino GND.
//  Pin 2: RX, connect to hp_rx_pin.
//  Pin 3: TX, connect to hp_tx_pin.
//  Pin 4: VCC, connect to Arduino 5V.
#define hp_rx_pin (8)
#define hp_tx_pin (9)

// A standard 16x2 "1602" LCD module.
// Pin 1: VSS, connect to Arduino GND.
// Pin 2: VDD, connect to Arduino 5V.
// Pin 3: VO (contrast):
//  Create a 0.6V reference by connecting Arduino 5V or 3.3V to a 10k resistor
//  to a diode to GND.  Connect VO to the 0.6V point of the reference.
// Pin 4: RS, connect to LCD_RS_pin.
// Pin 5: RW, connect to Arduino GND.
// Pin 6: E, connect to LCD_EN_pin.
// Pin 11: D4, connect to LCD_D4_pin.
// Pin 11: D5, connect to LCD_D5_pin.
// Pin 11: D6, connect to LCD_D6_pin.
// Pin 11: D7, connect to LCD_D7_pin.
// Pin 12: A (backlight LED anode):
//  Some 1602 boards need a current limiting resistor and some don't.
//  Connect a 220R from Arduino 5V to the A pin.  If it is very dim, try
//  omitting the resistor.
// Pin 13: K (backlight LED cathode), connect to Arduino GND.
#define LCD_RS_pin (3)
#define LCD_EN_pin (2)
#define LCD_D4_pin (4)
#define LCD_D5_pin (5)
#define LCD_D6_pin (6)
#define LCD_D7_pin (7)


#include <LiquidCrystal.h>
LiquidCrystal lcd(LCD_RS_pin, LCD_EN_pin, LCD_D4_pin, LCD_D5_pin, LCD_D6_pin, LCD_D7_pin);

#include <SoftwareSerial.h>
SoftwareSerial hp_serial(hp_rx_pin, hp_tx_pin);


void setup() {
    pinMode(LED_pin, OUTPUT);
    lcd.begin(16, 2);
    Serial.begin(9600);
    hp_serial.begin(9600);

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("HP 34401A");
    delay(1000);
}


// Data will stream from the 34401A in the following format:
// -9.34000000E-07\r\n
// +2.24900000E-06\r\n

#define BUF_LEN (17)  // e.g. '+2.24900000E-06\r\n'
char buf[BUF_LEN+1];

void loop() {
    // Reset to read the next value.
    memset(buf, '\0', BUF_LEN+1);
    int chars_read = 0;

    while (true) {
        // Spin until there is a char available to read.
        if (hp_serial.available() == 0) {
            continue;
        }

        // Read one char.
        char ch = hp_serial.read();

        // Handle the end of the line.
        if (ch == '\r' || ch == '\n') {
            // The line ending is '\r\n'.  Throw away the '\n'.
            if (chars_read == 0) {
                break;
            }

            // Convert the line to a float.
            float f = atof(buf);

            // Determine the exponent value, e.g. 'E-02' == 2.
            int exponent = (buf[14] - '0') + (10 * (buf[13] - '0'));
            if (buf[12] == '-') {
                exponent = -exponent;
            }

            // Format the value in non-scientific notation.
            char formatted[12+1];  // e.g. '-123456789.1', '-0.000000001'
            int dot_index = -1;
            // -1.0E-3 = -0.001
            // -1.0E-2 = -0.01
            // -1.0E-1 = -0.1
            // -1.0E0 = -1.0
            // -1.0E1 = -10.0
            // -1.0E2 = -100.0
            // -1.0E3 = -1000.0
            if (exponent < 1) {
                dot_index = 2;
            } else {
                dot_index = 2 + exponent;
            }
            formatted[0] = buf[0]; // the leading '+' or '-'.
            int in_index = 1;
            int out_index = 1;
            int trailing_zeros = 0;
            if (exponent < -1) {
                trailing_zeros = (-exponent) - 1; // e.g. if the exponent is -5, there will be 4 trailing zeros.
            }
            while (in_index < (11 /* the 'E' */ - trailing_zeros)) {
                if (in_index == 2 /* the '.' */) {
                    in_index += 1;
                    continue;
                } else if (out_index == dot_index) {
                    formatted[out_index] = '.';
                    out_index += 1;
                    continue;
                } else if (exponent < 0 && out_index < (-exponent)+2) {
                    formatted[out_index] = '0'; // leading zero's, e.g. 0.001.
                    out_index += 1;
                    continue;
                } else {
                    formatted[out_index] = buf[in_index];
                    in_index += 1;
                    out_index += 1;
                    continue;
                }
            }
            formatted[out_index] = '\0';

            // Format the value in non-scientific notation, with commas and underscores.
            char formatted2[14+1];  // e.g. '-123,456,789.1', '-0.000_000_001'
            int comma1_index = -1;
            int comma2_index = -1;
            int under1_index = -1;
            int under2_index = -1;
            if (exponent >= 6) { // at or above 6 we have two commas and no unders.
                // -1.0E7 = -10,000,000.0
                // -1.0E6 = -1,000,000.0
                dot_index += 2;
                comma1_index = exponent - 4;
                comma2_index = exponent;
            } else if (exponent == 4 || exponent == 5) { // for 4 and 5 we have one comma and no unders.
                // -1.0E+6 = -1,234,567.8
                // -1.0E+5 = -123,456.78
                // -1.0E+4 = -12,345.678
                // -1.0E+3 = -1,234.567_8
                dot_index += 1;
                comma1_index = exponent - 1;
            } else if (exponent == 3) { // for 3 we have one comma and one under.
                // -1.0E+4 = -12,345.678
                // -1.0E+3 = -1,234.567_8
                // -1.0E+2 = -123.456_78
                dot_index += 1;
                under1_index = 10;
            } else if (exponent == 1 || exponent == 2) { // for 2 and 1 we have no commas and one under.
                // -1.0E+3 = -1,234.567_8
                // -1.0E+2 = -123.456_78
                // -1.0E+1 = -12.345_678
                // -1.0E+0 = -1.234_567_8
                under1_index = exponent + 6;
            } else if (exponent <= 0) { // at or below zero, we no commas and two unders.
                // -1.0E+1 = -12.345_678
                // -1.0E+0 = -1.234_567_8
                // -1.0E-1 = -0.123_456_78
                // -1.0E-2 = -0.012_345_678
                // -1.0E-3 = -0.001
                // -1.0E-4 = -0.000_1
                // -1.0E-5 = -0.000_01
                under1_index = 6;
                under2_index = 10;
            }
            formatted2[0] = buf[0]; // the leading '+' or '-'.
            in_index = 1;
            out_index = 1;
            int copied_digits = 0;
            while (in_index < (11 /* the 'E' */ - trailing_zeros)) {
                if (in_index == 2 /* the '.' */) {
                    in_index += 1;
                    continue;
                } else if (out_index == dot_index) {
                    formatted2[out_index] = '.';
                    out_index += 1;
                    continue;
                } else if (out_index == comma1_index || out_index == comma2_index) {
                    formatted2[out_index] = ',';
                    out_index += 1;
                    continue;
                } else if (out_index == under1_index || out_index == under2_index) {
                    formatted2[out_index] = ',';
                    out_index += 1;
                    continue;
                } else if (exponent < 0 && out_index < (-exponent)+2) {
                    formatted2[out_index] = '0'; // leading zero's, e.g. 0.001.
                    out_index += 1;
                    continue;
                } else if (exponent <= -5 && out_index < (-exponent)+3) {
                    formatted2[out_index] = '0'; // leading zero's, e.g. 0.001.
                    out_index += 1;
                    continue;
                } else {
                    formatted2[out_index] = buf[in_index];
                    in_index += 1;
                    out_index += 1;
                    copied_digits += 1;
                    if (copied_digits == 8) {
                        break;
                    }
                    continue;
                }
            }
            formatted2[out_index] = '\0';

            // Send the formatted value out the (hardware) serial port.
            Serial.print(formatted);
            Serial.print("\n");
            digitalWrite(LED_pin, LOW);

            // Print the formatted value on the second line of the LCD.
            lcd.setCursor(0, 1);
            lcd.print(formatted2);
            break;
        }

        // Accumulate chars into the buffer and echo them to the LCD.
        digitalWrite(LED_pin, HIGH);
        buf[chars_read] = ch;
        if (chars_read == 0) {
            lcd.clear();
        }
        lcd.setCursor(chars_read, 0);
        lcd.print(ch);
        chars_read += 1;
        continue;
    }
}
	// hp34401a-lcd.ino: Arduino sketch to display HP 34401A readings on a 16x2 LCD
	// as well as send them out the serial port.

	// Copyright 2022 Jason Pepas.
	// Released under the terms of the MIT License.
	// See https://opensource.org/licenses/MIT.

	// Setup:

	// First, set your 34401A to "talk only" mode:
	// Menu -> I/O Menu -> HP-IB Addr -> 31.

	// Next, prepare a RS232-to-TTL adapter by soldering a pull-up resistor from
	// the DB9 pin 6 (the DSR pin) to VCC (5V).
	// See https://gist.github.com/cellularmitosis/1582236f226e9d98075a0c971eb4168c for soldering details.

	// Thanks to:
	// https://www.eevblog.com/forum/testgear/external-display-for-agilent-34401a-(or-any-dmm-with-rs232-output-stream)/msg326470/#msg326470
	// "Set DB9 pin 6 DSR high 5V"


	// Pins:

	#define LED_pin (13) // The onboard Arduino LED.

	// The RS232-to-TTL adapter will have four pins:
	// Pin 1: GND, connect to Arduino GND.
	// Pin 2: RX, connect to hp_rx_pin.
	// Pin 3: TX, connect to hp_tx_pin.
	// Pin 4: VCC, connect to Arduino 5V.
	#define hp_rx_pin (8)
	#define hp_tx_pin (9)

	// A standard 16x2 "1602" LCD module.
	// Pin 1: VSS, connect to Arduino GND.
	// Pin 2: VDD, connect to Arduino 5V.
	// Pin 3: VO (contrast):
	// Create a 0.6V reference by connecting Arduino 5V or 3.3V to a 10k resistor
	// to a diode to GND. Connect VO to the 0.6V point of the reference.
	// Pin 4: RS, connect to LCD_RS_pin.
	// Pin 5: RW, connect to Arduino GND.
	// Pin 6: E, connect to LCD_EN_pin.
	// Pin 11: D4, connect to LCD_D4_pin.
	// Pin 11: D5, connect to LCD_D5_pin.
	// Pin 11: D6, connect to LCD_D6_pin.
	// Pin 11: D7, connect to LCD_D7_pin.
	// Pin 12: A (backlight LED anode):
	// Some 1602 boards need a current limiting resistor and some don't.
	// Connect a 220R from Arduino 5V to the A pin. If it is very dim, try
	// omitting the resistor.
	// Pin 13: K (backlight LED cathode), connect to Arduino GND.
	#define LCD_RS_pin (3)
	#define LCD_EN_pin (2)
	#define LCD_D4_pin (4)
	#define LCD_D5_pin (5)
	#define LCD_D6_pin (6)
	#define LCD_D7_pin (7)


	#include <LiquidCrystal.h>
	LiquidCrystal lcd(LCD_RS_pin, LCD_EN_pin, LCD_D4_pin, LCD_D5_pin, LCD_D6_pin, LCD_D7_pin);

	#include <SoftwareSerial.h>
	SoftwareSerial hp_serial(hp_rx_pin, hp_tx_pin);


	void setup() {
	pinMode(LED_pin, OUTPUT);
	lcd.begin(16, 2);
	Serial.begin(9600);
	hp_serial.begin(9600);

	lcd.clear();
	lcd.setCursor(0, 0);
	lcd.print("HP 34401A");
	delay(1000);
	}


	// Data will stream from the 34401A in the following format:
	// -9.34000000E-07\r\n
	// +2.24900000E-06\r\n

	#define BUF_LEN (17) // e.g. '+2.24900000E-06\r\n'
	char buf[BUF_LEN+1];

	void loop() {
	// Reset to read the next value.
	memset(buf, '\0', BUF_LEN+1);
	int chars_read = 0;

	while (true) {
	// Spin until there is a char available to read.
	if (hp_serial.available() == 0) {
	continue;
	}

	// Read one char.
	char ch = hp_serial.read();

	// Handle the end of the line.
	if (ch == '\r' \|\| ch == '\n') {
	// The line ending is '\r\n'. Throw away the '\n'.
	if (chars_read == 0) {
	break;
	}

	// Convert the line to a float.
	float f = atof(buf);

	// Determine the exponent value, e.g. 'E-02' == 2.
	int exponent = (buf[14] - '0') + (10 * (buf[13] - '0'));
	if (buf[12] == '-') {
	exponent = -exponent;
	}

	// Format the value in non-scientific notation.
	char formatted[12+1]; // e.g. '-123456789.1', '-0.000000001'
	int dot_index = -1;
	// -1.0E-3 = -0.001
	// -1.0E-2 = -0.01
	// -1.0E-1 = -0.1
	// -1.0E0 = -1.0
	// -1.0E1 = -10.0
	// -1.0E2 = -100.0
	// -1.0E3 = -1000.0
	if (exponent < 1) {
	dot_index = 2;
	} else {
	dot_index = 2 + exponent;
	}
	formatted[0] = buf[0]; // the leading '+' or '-'.
	int in_index = 1;
	int out_index = 1;
	int trailing_zeros = 0;
	if (exponent < -1) {
	trailing_zeros = (-exponent) - 1; // e.g. if the exponent is -5, there will be 4 trailing zeros.
	}
	while (in_index < (11 /* the 'E' */ - trailing_zeros)) {
	if (in_index == 2 /* the '.' */) {
	in_index += 1;
	continue;
	} else if (out_index == dot_index) {
	formatted[out_index] = '.';
	out_index += 1;
	continue;
	} else if (exponent < 0 && out_index < (-exponent)+2) {
	formatted[out_index] = '0'; // leading zero's, e.g. 0.001.
	out_index += 1;
	continue;
	} else {
	formatted[out_index] = buf[in_index];
	in_index += 1;
	out_index += 1;
	continue;
	}
	}
	formatted[out_index] = '\0';

	// Format the value in non-scientific notation, with commas and underscores.
	char formatted2[14+1]; // e.g. '-123,456,789.1', '-0.000_000_001'
	int comma1_index = -1;
	int comma2_index = -1;
	int under1_index = -1;
	int under2_index = -1;
	if (exponent >= 6) { // at or above 6 we have two commas and no unders.
	// -1.0E7 = -10,000,000.0
	// -1.0E6 = -1,000,000.0
	dot_index += 2;
	comma1_index = exponent - 4;
	comma2_index = exponent;
	} else if (exponent == 4 \|\| exponent == 5) { // for 4 and 5 we have one comma and no unders.
	// -1.0E+6 = -1,234,567.8
	// -1.0E+5 = -123,456.78
	// -1.0E+4 = -12,345.678
	// -1.0E+3 = -1,234.567_8
	dot_index += 1;
	comma1_index = exponent - 1;
	} else if (exponent == 3) { // for 3 we have one comma and one under.
	// -1.0E+4 = -12,345.678
	// -1.0E+3 = -1,234.567_8
	// -1.0E+2 = -123.456_78
	dot_index += 1;
	under1_index = 10;
	} else if (exponent == 1 \|\| exponent == 2) { // for 2 and 1 we have no commas and one under.
	// -1.0E+3 = -1,234.567_8
	// -1.0E+2 = -123.456_78
	// -1.0E+1 = -12.345_678
	// -1.0E+0 = -1.234_567_8
	under1_index = exponent + 6;
	} else if (exponent <= 0) { // at or below zero, we no commas and two unders.
	// -1.0E+1 = -12.345_678
	// -1.0E+0 = -1.234_567_8
	// -1.0E-1 = -0.123_456_78
	// -1.0E-2 = -0.012_345_678
	// -1.0E-3 = -0.001
	// -1.0E-4 = -0.000_1
	// -1.0E-5 = -0.000_01
	under1_index = 6;
	under2_index = 10;
	}
	formatted2[0] = buf[0]; // the leading '+' or '-'.
	in_index = 1;
	out_index = 1;
	int copied_digits = 0;
	while (in_index < (11 /* the 'E' */ - trailing_zeros)) {
	if (in_index == 2 /* the '.' */) {
	in_index += 1;
	continue;
	} else if (out_index == dot_index) {
	formatted2[out_index] = '.';
	out_index += 1;
	continue;
	} else if (out_index == comma1_index \|\| out_index == comma2_index) {
	formatted2[out_index] = ',';
	out_index += 1;
	continue;
	} else if (out_index == under1_index \|\| out_index == under2_index) {
	formatted2[out_index] = ',';
	out_index += 1;
	continue;
	} else if (exponent < 0 && out_index < (-exponent)+2) {
	formatted2[out_index] = '0'; // leading zero's, e.g. 0.001.
	out_index += 1;
	continue;
	} else if (exponent <= -5 && out_index < (-exponent)+3) {
	formatted2[out_index] = '0'; // leading zero's, e.g. 0.001.
	out_index += 1;
	continue;
	} else {
	formatted2[out_index] = buf[in_index];
	in_index += 1;
	out_index += 1;
	copied_digits += 1;
	if (copied_digits == 8) {
	break;
	}
	continue;
	}
	}
	formatted2[out_index] = '\0';

	// Send the formatted value out the (hardware) serial port.
	Serial.print(formatted);
	Serial.print("\n");
	digitalWrite(LED_pin, LOW);

	// Print the formatted value on the second line of the LCD.
	lcd.setCursor(0, 1);
	lcd.print(formatted2);
	break;
	}

	// Accumulate chars into the buffer and echo them to the LCD.
	digitalWrite(LED_pin, HIGH);
	buf[chars_read] = ch;
	if (chars_read == 0) {
	lcd.clear();
	}
	lcd.setCursor(chars_read, 0);
	lcd.print(ch);
	chars_read += 1;
	continue;
	}
	}