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Lisp Badge: A single-board computer that you can program in uLisp

The Lisp Badge is a self-contained computer with its own display and keyboard, based on an ATmega1284, that you can program in uLisp:


You can use it to run programs that interface to components such as LEDs and push-buttons via the I/O pins, read the analogue inputs, and operate external devices via the I2C and SPI interfaces. It has a greyscale OLED display that gives 8 lines of 42 characters, and an integrated 45-key keyboard optimised for Lisp.

For details of how to build one see Lisp Badge on Technoblogy.


Size: 107mm x 61mm (4.2″ x 2.4″).

Display: 42 characters x 8 lines.

Keyboard: Integrated 45-key keyboard providing upper and lower-case characters, digits, and the symbols required by uLisp.

Memory available: 2816 Lisp cells (11264 bytes).

EEPROM: 1024 Lisp cells (4096 bytes), allows you to save the Lisp workspace using save-image.

Processor: ATmega1284P

Clock speed: 16 MHz.

Current consumption: Approx. 20 mA.


uLisp, a subset of Common Lisp, with 122 Lisp functions and special forms. For a full definition see uLisp Language Reference.

The language includes two extensions, plot and plot3d, for plotting graphs and 3d functions. 

Types supported: list, symbol, integer, character, string, and stream.

An integer is a sequence of digits, optionally prefixed with “+” or “-“. Integers can be between -32768 and 32767. You can enter numbers in hexadecimal, octal, or binary with the notations #x2A, #o52, or #b101010, all of which represent 42.

User-defined symbol names can have arbitrary names. Any sequence that isn’t an integer can be used as a symbol; so, for example, 12a is a valid symbol.

There is one namespace for functions and variables; in other words, you cannot use the same name for a function and a variable.

Includes a mark and sweep garbage collector. Garbage collection takes 5 msec.


These interfaces are brought to headers at the edge of the Lisp Badge board. The numbers in brackets refer to Arduino pin numbers:

  • Four analogue input pins using analogread: A0 to A3 (24 to 27) plus VCC and GND.
  • Two analogue outputs using analogwrite: MISO (6), and SCK (7).
  • Digital input and output using pinmode, digitalread, and digitalwrite: MOSI (5), MISO (6), SCK (7), RX0 (8), TX0 (9), SCL (16), SDA (17), and A0 to A3 (24 to 27)
  • I2C interface using with-i2c and restart-i2c: SCL (16) and SDA (17).
  • SPI interface using with-spi: MOSI (5), MISO (6), and SCK (7).
  • Serial interface (FTDI) using with-serial: RX0 (8) and TX0 (9).

The shift key can be used as a digital input: SHIFT (23).

SCK (7) is connected to an LED on the front panel. This is an analogue output pin, so you can vary the brightness of the LED.

Plotting extensions

The Lisp Badge contains two plotting extensions, plot and plot3d, designed to allow plotting to the greyscale graphics display.

After generating a plot both functions wait for the ESC key to be pressed before displaying the uLisp prompt.

plot function

Syntax: (plot [x-intercept y-intercept] [function]...)

Plots up to four functions on the same graph, optionally with axes.

Each function should be a function of one parameter, the x coordinate, and it will be called with each value of x from 0 to 255. The function should return the y value, from 0 to 63.

If x-intercept and y-intercept are specified, plot3d draws axes through those intercepts.

For example, defining:

(defun sine ()
  (let ((x 0) (y 2045))
    (lambda (n) 
      (incf x (/ (* y 16) 163))
      (decf y (/ (* x 16) 163))
    (+ 32 (ash x -6)))))

the following command:

(plot 0 32 (sine))

will plot:


Plotting multiple functions

The following example plots the voltages on the analogue inputs 0 to 3 once a second on a single plot. First define:

(defun adc (n) (lambda (x) (delay 250) (/ (analogread n) 8)))

Then give the command:

(plot 0 0 (adc 0) (adc 1) (adc 2) (adc 3))

plot3d function

Syntax: (plot3d [x-intercept y-intercept] [function])

The function should be a function of two parameters, the x and y coordinates, and it will be called with each value of x from 0 to 255 and y from 0 to 63. The function should return the greyscale value to be plotted, from 0 to 15.

If x-intercept and y-intercept are specified, plot3d draws axes through those intercepts.

For example, defining:

(defun p (x y) 
  (let ((a (/ (- x 128) 2))
        (b (- y 32))) 
    (min (abs (- (logand (/ (+ (* a a) (* b b) (* a b)) 16) 31) 15)) 15)))

the following command:

(plot3d 128 32 p)

will plot:


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