Tag: radio

LED interface for rx-320 receiver

implementation of low resolution LED interface for TenTec rx-320 receiver.

Based on this design: http://reactivemusic.net/?p=12408


(note: this work is in progress. The github version has not been tested)


folder: max/LED-project/


  • ab-rx320-g02.maxpat (main patch)
  • colorpanel.pat
  • palette.txt
  • mod_engine_d.pat
  • mod_fb_router.pat
  • panel2.js
  • rxpanel2.mxb
  • rxsynth.xml
Note the BCR-2000 preset is not yet available


  • Behringer BCR-2000 Midi controller
  • 2 TenTec rx-320 receivers
  • 2 USB to serial adapters


(in progress)

Connect all the hardware and open ab-rx320-g02 in Max.

Set the MIDI and serial ports as directed in the patch.


The system uses two TenTec  rx-320 radios, controlled by Max. Here is some of the data that is displayed.

  • frequency in Hz.
  • gain
  • filter setting
  • mode (AM/SSB)
  • Passband shift
  • BFO
  • frequency calibration
  • AGC
  • Mute
  • scan-mode
  • memory presets
  • data rate (speed limit)
  • time clock
  • memory preset selection
  • 5 modulator units
  • indicators that show which radio parameters are getting modulated
  • and others…
Modulator unit detail
control interface

A Behringer BCR2000 provides  User input to the radio. Here is a rough layout of the controls:

Button detail

Note there have been changes: Auto cal is now s-match

 memory preset categories

 blobs (display units)

modulator destinations (it doesn’t seem to be working like this…)

memory presets – search results:

what’s next
  • Need to clean up the control interface – build a template for bcd-2000
  • better documentation of LED interface
  • write instructions
  • more testing
local files

tkzic/max new radio project

main patch: ab-rx320-g02.maxpat


Low resolution LED interface

Lots of information in a few pixels.

Computer displays have evolved to high resolutions. What about the other direction? This experiment  is a display interface using a grid of LED’s. Essentially, very large pixels.

information types
  • on/off 
  • small numbers (0-10)
  • large numbers (0-10,000,000)
  • clocks
  • level indicators
  • connections
  • map keys (i.e., explanations of symbols) 
communicating with LED’s

LED’s communicate information using

  • brightness
  • color
  • movement

With just a few LED’s its easy to display a clear message. A large matrix of LEDS can get confusing. Here are a few suggestions:

  • Use separate regions for each block of information.
  • Draw guide markers to help locate positions by giving frame of reference.
  • Animation catches the eye but also distracts, and confuses.


traffic lights

An effective but inefficient signaling method.

resistor codes:

Resistors use a numeric color code.

Find the value of any resistor by looking at the first four 4 color bands. Colors represent  base 10 exponential notation.


An abacus uses 5 or 10 beads for each digit. Faster than decoding a resistor and works with one color – but takes up more space.

level meters

Segmented level meters convey information using a line of pixels:

binary clock

Represents digits using binary coded decimal notation.

An LED grid in Max

This grid design was used for the visual interface of a shortwave radio:

And an etch-a-sketch:



folder: LED-display/rx-320/


  • rxpanel2.maxpat (main patch)
  • panel2.js (javascript)


There are 2 large toggles – one for etch-a-sketch, and another for the radio simulator. Try one, then toggle it off before trying another one. If you forget – just restart the patch.

The number box near the top can be used to expand or contract the display size (while it is active) The default size is 17.

how it works

The same patch generated both video examples above. It uses javascript to make a two dimensional array of Max led objects. Each object is addressable by its position in the array. Here’s the code to make the objects:

// makecells - create matrix of led objects
function makecells( x, y, color )

var p;		// this patcher
var tmpstr;
var objname;

	post( "makecells: ", x, y, color );
	post( );

	p = this.patcher;

// make cells

	for( i = 0; i < x; i++ )
		for(j = 0; j < y; j++ )
			cell[i][j] = p.newdefault(xorigin + (i * cellspace), yorigin + (j * cellspace), "led" );    // create leds
			if(color != 9 )
				cell[i][j].hidden = 0;
				cell[i][j].message( "pict", color );
				cell[i][j].hidden = 1;

			cell[i][j].varname = "led" + i + "x" +  j;							//  assigns name for future use	




Although each LED in a grid is addressable, its easier to group sections of the grid into blobs. Each blob is a unit that displays data, like a number for example. There are several types of blobs:

Here are the properties of a blob:

//  blob data structure
//   x, y upper left
//   lengthx, lengthy, 
//   orientation: 0 = horizontal, 1 = vertical
//   step  1 = downward or rightward,  -1 = upward or leftward  (this defines the corner of origin too)
//   data lorange, hirange
//   scale: 0 = no, 1 = yes
//   blobtype: 0 = generic decimal,  1 = spare,  2 = pushbutton flash,  3 = radiobutton, 
//   color code 0-9
//   contrast color 0-9
//   signed ( 0 = no, 1 = yes)		// booooooooooooooolean  
//   colorshift ( 0 = normal , 1 = use different colors every 3 digits, like comma separators (frequency display)
//   blink  (milliseconds duration for pushbutton flash type only (led blinktime )
//   radio number
//   name
//   value


Blob data examples

Lets look at examples of various ways to display data – as used in the shortwave radio video above.

Here are 3 blobs that represent numbers in three different ways.

The far left column and the bottom row are key graphics. They give a frame of reference for the data.


Moving from left to right…

The LED’s far left column, are a graphic key, starting with red on the bottom, represent the numbers 1-9

The next blue column is just a divider

The 3rd column of white dots is the signal strength data ranging from the 0-9. The current value is ‘4’, represented by a column of 4 dots.

The next nine columns (4-12) represent the frequency in Hz. ranging from 0-999,999,999. The data is in groups of three (as you can see by looking at the graphical key in the bottom row). The number currently displayed is: 4,999,991.

Negative frequencies are displayed by shifting the colors to values that don’t match the key graphic.

The last column is a radio button with 4 possible values and is currently set to ‘3’


The bottom row is a key graphic, showing a different color, or group of colors for each data item. So for example, there is one white dot under the signal strength data in column 3. There are 3 groups of 3 dots (yellow, green, yellow) in columns 4-12 representing the frequency data in the format: 999,999,999.

The 2nd blue row from the bottom is a divider.

The next shows which data items are being controlled by modulators. The 3 white LED’s show modulation of frequency data in the million’s, 100’s, and ten’s  places.

Modulator units

There are 5 modulator units in the display. Data is represented using a color code..

  1.  red
  2. green
  3. blue
  4. yellow
  5. white

Gray LED’s represent ‘momentary’ controls in the off state. When a momentary button is pressed, it will blink white.

Here is an example of a modulator unit

The blue LED’s are just dividers (background space)


The first column of data on the left is the on/off indicator and the modulator’s ID number.

The top LED of the column is the on/off toggle. It is blank, which means off.

The next two red LED’s together represent the ID number of the modulator: red = 1

For the remaining columns, the top row indicates whether the input gate is open allowing other modulators to control the parameter. Grey indicates the gate is closed, A white LED means the input gate is open.

The second and third columns of data are the clock speed and wave type. The 2 LEDS in each column are grouped together and are using the color code above. The clock speed is 5 (white). The wave type is 4 (yellow)

The fourth and fifth columns of data are the low and high range. Low range value is 5 (white) and high range value is 2 (green) – which doesn’t make sense, but this is simulator data.

The last column is the modulator destination activity indicator: grey if zero (not assigned) or white if any non-zero value.

modulator data structure:
// modulator data structure
// these are fixed structures 8x2, with specific color rules
// ulx, uly
// mod id number 1-n 
// on	: 0 = off, 1 = on
// modin :  modulation source index 0-4
// clockspeed  :  0-4
// wavetype : 0-4
// lorange : 0-4
// hirange : 0-4
// ingate : 0 - 4  (tells which control is being modulated)
// spare
// destination : 0-127 destination index  // this is displayed elsewhere


hardware interface

Adafruit 32×32 RGB LED panel


local file notes:

files are also in tkzic/new max radio project/

There is a newer version adapted for the Max radio project – basically same code, but file names are

  • rxpanel3.maxpat
  • panel3.js


rx-320 control

Operate the TenTec rx-320 receiver in Max.

A simple control program. Features save/recall memory presets with random scanning.



folder: max/receiver


  • Click the print message near the serial object to get a list of the serial ports in the Max window
  • Unlock the patch and edit the serial object to use the correct port letter


  • runs in Mac OS and Windows
  • It would be worth checking the code that sets frequency and BFO against the newer code in the LED-project. I can’t remember if I updated this older version
  • There is also a version of this program that runs with ICOM ic-746 receiver

VCR’s are analog TV transmitters

Any VCR with antenna output has a built-in RF modulator.

Generally they transmit on channels 2-4. Here are the US frequencies:

from wikipedia http://en.wikipedia.org/wiki/Television_channel_frequencies

The signal is weak, not intended for broadcast. Not legal to broadcast… but hypothetically, amplifiers and antennas could be connected.

This audio signal is from an iPod playing through a VCR received by rtl-sdr in Max on 65.75 MHz. (channel 3) using a random length wire connected to the antenna output.


Notes about RF modulators:

I have tried this with some small RF modulator boxes. One of the problems is that you need to send a signal to the video input, or the modulator won’t run. You can get a rough signal by patching one of the audio channels into the video input jack. Or a better signal by using the video composite output of a raspberry-pi. Although the VCR gives a much cleaner signal

LM386N audio preamp circuit

Here’s a circuit that provides some gain to iPod line-out audio to drive the TXD pin of a Radiometrix NTX2. It uses an LM386N audio amplifier chip (available from Radio Shack).  I just substituted capacitors until it worked. Its powered by +5v DC from an Arduino pin.

Roughly based on this circuit –  http://www.instructables.com/image/FTZUHWBGD2J36P8

Next will be trying the TS922 op amp.