… or what you get if you video concentric RGB LED rings and put them out of focus.
The All-Seeing Googly Eyes of Lisa Frank
Tag: led
Blinking on and off with the 74LS42
I want to make an edge-lit numeric display. These were a common technology before numeric LEDs were available. They use 10 illuminated slides to display individual numbers. Here’s my first try at the display:
The 74LS42 logic chip (4-Line BCD to 10-Line Decimal Decoder) seems a likely candidate to drive such a display. You feed it a 4-bit binary-coded decimal input, and the chip activates one of ten outputs. It’s a low-voltage version of the old 7441 chip used for driving Nixie tubes. Here’s what I got working as a demo of the 7442, driven by an Arduino:
(Video link for the iframe-averse: https://www.youtube.com/watch?v=cETGB2M8iUw)
From the video you can see that:
- The 7442 only passes inputs from 0 (0000b) to 9 (1001b). All other inputs result in no output.
- The outputs are really more like 1–10 than 0–9, as a zero input activates the first output.
Making a clean breadboard layout for this circuit was a little more work than I’d anticipated. It just fits on a half-sized breadboard:
Because the 7442 will only activate one output at a time, it’s okay to use a single current-limiting resistor for all ten output LEDs. The chip also uses active low outputs: the outputs go from high to low when activated. The negative side of each LED goes to an output pin, and the chip sinks current when an output is selected, lighting the LED.
The components get in the way of seeing the wiring, so here’s another picture from Fritzing with just the wires and the breadboard:
Apart from the 74LS42 chip itself, the components I used were 10× 3mm orange LEDs on the outputs and 4× 3mm green LEDs on the inputs. I don’t have a spec for them (they were from a bargain selection box from PCBoard.ca) so my use of ridiculously precise 332 Ω 1% resistors to limit current is a little unnecessary. (I have a bunch of these precision resistors from a project that didn’t go ahead, so using them is cheaper for me than digging about for a 5% one.)
Finally, here’s the Arduino sketch I wrote to drive the chip for the demo video. All it does is cycle through digital outputs 4–7, incrementing a bit every half second.
/*
SeventyfourFortytwo - Arduino demo of a
74LS42 - 4-line BCD to 10-line decimal decoder
Steps through 0-15, two steps per second
Shows the 74LS42's blocking of values 10-15 as invalid
Wiring:
Arduino 74LS42
======== =======
4 - 15 Input A (bit 0)
5 - 14 Input B (bit 1)
6 - 13 Input C (bit 2)
7 - 12 Input D (bit 3)
scruss - 2016-09-23
*/
int n = 0;
void setup() {
pinMode(4, OUTPUT);
pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
pinMode(7, OUTPUT);
digitalWrite(4, LOW);
digitalWrite(5, LOW);
digitalWrite(6, LOW);
digitalWrite(7, LOW);
}
void loop() {
digitalWrite(4, n & 1);
digitalWrite(5, n & 2);
digitalWrite(6, n & 4);
digitalWrite(7, n & 8);
n++;
if (n > 15) n = 0;
delay(500);
}
If you felt really fancy, you could drive the LED inputs through PWM, and come up with just the right of flicker to make this look like a Nixie tube. You should also be able to chain the inputs through some shift registers, too.
Work-in-progress: Sayso Globord audio decoding
You may still be able to get surplus Sayso Globord programmable LED signs in surplus stores. It’s a 7×24 LED scrolling sign that you can program with a lightpen or with audio input.
The unit comes with no software, but has a link to https://www.dropbox.com/sh/q1q9yhahwtblb23/AACpMeXQjYyD8ZWC-65vNgcxa printed on the box. It’s an archive of the programming software, manual, and canned audio files for a whole bunch of standard messages. Here’s an archive if the dropbox link goes away: SaySo.zip
The audio files used for programming the display are clearly FSK-encoded, but I haven’t quite worked out the relationship between the tones and the display bits. Here’s what I’ve worked out so far:
- Files are made up of 12 audio blocks, each about 0.9 seconds long. Each block appears to correspond to one 7×24 display screen.
- Mark (1 bit): Three cycles, 96 samples at 44100 Hz: 1378.125 Hz
- Space (0 bit): Four cycles, 256 samples at 44100 Hz: 689.0625 Hz
The editor runs nicely under DOSBox, so you can experiment and save samples as WAV files. Here’s a sample display with its corresponding audio linked underneath:
I’m not sure how much extra work I have time or inclination to put in on getting this working, but I hope that my preliminary work will be useful to someone (maybe this person).
python + Arduino + Tk: Toggling an LED
Phil sent me a note last week asking how to turn an LED on or off using Python talking through Firmata to an Arduino. This was harder than it looked.
It turns out the hard part is getting the value from the Tkinter Checkbutton itself. It seems that some widgets don’t return values directly, so you must read the widget’s value with a get() method. This appears to work:
#!/usr/bin/python
# turn an LED on/off with a Tk Checkbutton - scruss 2012/11/13
# Connection:
# - small LED connected from D3, through a resistor, to GND
import pyfirmata
from Tkinter import *
# Create a new board, specifying serial port
# board = pyfirmata.Arduino('/dev/ttyACM0') # Raspberry Pi
board = pyfirmata.Arduino('/dev/tty.usbmodem411') # Mac
root = Tk()
var = BooleanVar()
# set up pins
pin3 = board.get_pin('d:3:o') # D3 On/Off Output (LED)
def set_led(): # set LED on/off
ledval = var.get()
print "Toggled", ledval
pin3.write(ledval)
# now set up GUI
b = Checkbutton(root, text = "LED", command = set_led,
variable = var)
b.pack(anchor = CENTER)
root.mainloop()
This is explained quite well here: Tkinter Checkbutton doesn’t change my variable – Stack Overflow. I also learnt a couple of things about my previous programs:
- You don’t really need to set up an Iterator unless you’re reading analogue inputs
- My “clever” cleanup-on-exit code actually made the script hang on Mac OS.
♡
(Arduino + LoL Shield + hand drawn 14×9 GIFs [
,
, and 
] + this)
much improved HSV colour cycling LED on Arduino
There were some flaws in the post HSV colour cycling LED on Arduino. This does much more what I wanted:
/* HSV fade/bounce for Arduino - Stewart C. Russell - scruss.com - 2010/09/19 Wiring: LED is RGB common cathode (SparkFun sku: COM-09264 or equivalent) * Digital pin 9 → 165Ω resistor → LED Red pin * Digital pin 10 → 100Ω resistor → LED Green pin * Digital pin 11 → 100Ω resistor → LED Blue pin * GND → LED common cathode. */ #define RED 9 // pin for red LED; green on RED+1 pin, blue on RED+2 pin #define DELAY 2 long rgb[3]; long rgbval, k; float hsv[3] = { 0.0, 0.5, 0.5 }; float hsv_min[3] = { 0.0, 0.0, 0.4 // keep V term greater than 0 for smoothness }; float hsv_max[3] = { 6.0, 1.0, 1.0 }; float hsv_delta[3] = { 0.0005, 0.00013, 0.00011 }; /* chosen LED SparkFun sku: COM-09264 has Max Luminosity (RGB): (2800, 6500, 1200)mcd so we normalize them all to 1200 mcd - R 1200/2800 = 0.428571428571429 = 109/256 G 1200/6500 = 0.184615384615385 = 47/256 B 1200/1200 = 1.0 = 256/256 */ long bright[3] = { 109, 47, 256 }; void setup () { randomSeed(analogRead(4)); for (k=0; k<3; k++) { pinMode(RED + k, OUTPUT); rgb[k]=0; // start with the LED off analogWrite(RED + k, rgb[k] * bright[k]/256); if (k>1 && random(100) > 50) { // randomly twiddle direction of saturation and value increment on startup hsv_delta[k] *= -1.0; } } } void loop() { for (k=0; k<3; k++) { // for all three HSV values hsv[k] += hsv_delta[k]; if (k<1) { // hue sweeps simply upwards if (hsv[k] > hsv_max[k]) { hsv[k]=hsv_min[k]; } } else { // saturation or value bounce around if (hsv[k] > hsv_max[k] || hsv[k] < hsv_min[k]) { hsv_delta[k] *= -1.0; hsv[k] += hsv_delta[k]; } } hsv[k] = constrain(hsv[k], hsv_min[k], hsv_max[k]); // keep values in range } rgbval=HSV_to_RGB(hsv[0], hsv[1], hsv[2]); rgb[0] = (rgbval & 0x00FF0000) >> 16; // there must be better ways rgb[1] = (rgbval & 0x0000FF00) >> 8; rgb[2] = rgbval & 0x000000FF; for (k=0; k<3; k++) { // for all three RGB values analogWrite(RED + k, rgb[k] * bright[k]/256); } delay(DELAY); } long HSV_to_RGB( float h, float s, float v ) { /* modified from Alvy Ray Smith's site: http://www.alvyray.com/Papers/hsv2rgb.htm H is given on [0, 6]. S and V are given on [0, 1]. RGB is returned as a 24-bit long #rrggbb */ int i; float m, n, f; // not very elegant way of dealing with out of range: return black if ((s<0.0) || (s>1.0) || (v<0.0) || (v>1.0)) { return 0L; } if ((h < 0.0) || (h > 6.0)) { return long( v * 255 ) + long( v * 255 ) * 256 + long( v * 255 ) * 65536; } i = floor(h); f = h - i; if ( !(i&1) ) { f = 1 - f; // if i is even } m = v * (1 - s); n = v * (1 - s * f); switch (i) { case 6: case 0: // RETURN_RGB(v, n, m) return long(v * 255 ) * 65536 + long( n * 255 ) * 256 + long( m * 255); case 1: // RETURN_RGB(n, v, m) return long(n * 255 ) * 65536 + long( v * 255 ) * 256 + long( m * 255); case 2: // RETURN_RGB(m, v, n) return long(m * 255 ) * 65536 + long( v * 255 ) * 256 + long( n * 255); case 3: // RETURN_RGB(m, n, v) return long(m * 255 ) * 65536 + long( n * 255 ) * 256 + long( v * 255); case 4: // RETURN_RGB(n, m, v) return long(n * 255 ) * 65536 + long( m * 255 ) * 256 + long( v * 255); case 5: // RETURN_RGB(v, m, n) return long(v * 255 ) * 65536 + long( m * 255 ) * 256 + long( n * 255); } }
HSV colour cycling LED on Arduino
Pretty much everyone tries the RGB colour cycler when they get their first Arduino. This variant cycles through the HSV colour wheel, though at fixed saturations and values.
Code:
// HSV fade/bounce for Arduino - scruss.com - 2010/09/12
// Note that there's some legacy code left in here which seems to do nothing
// but should do no harm ...
// don't futz with these, illicit sums later
#define RED 9 // pin for red LED
#define GREEN 10 // pin for green - never explicitly referenced
#define BLUE 11 // pin for blue - never explicitly referenced
#define SIZE 255
#define DELAY 10
#define HUE_MAX 6.0
#define HUE_DELTA 0.01
long deltas[3] = {
5, 6, 7 };
long rgb[3];
long rgbval;
// for reasons unknown, if value !=0, the LED doesn't light. Hmm ...
// and saturation seems to be inverted
float hue=0.0, saturation=1.0, value=1.0;
/*
chosen LED SparkFun sku: COM-09264
has Max Luminosity (RGB): (2800, 6500, 1200)mcd
so we normalize them all to 1200 mcd -
R 1200/2800 = 0.428571428571429 = 109/256
G 1200/6500 = 0.184615384615385 = 47/256
B 1200/1200 = 1.0 = 256/256
*/
long bright[3] = {
109, 47, 256};
long k, temp_value;
void setup () {
randomSeed(analogRead(4));
for (k=0; k<3; k++) {
pinMode(RED + k, OUTPUT);
rgb[k]=0;
analogWrite(RED + k, rgb[k] * bright[k]/256);
if (random(100) > 50) {
deltas[k] = -1 * deltas[k]; // randomize direction
}
}
}
void loop() {
hue += HUE_DELTA;
if (hue > HUE_MAX) {
hue=0.0;
}
rgbval=HSV_to_RGB(hue, saturation, value);
rgb[0] = (rgbval & 0x00FF0000) >> 16; // there must be better ways
rgb[1] = (rgbval & 0x0000FF00) >> 8;
rgb[2] = rgbval & 0x000000FF;
for (k=0; k<3; k++) { // for all three colours
analogWrite(RED + k, rgb[k] * bright[k]/256);
}
delay(DELAY);
}
long HSV_to_RGB( float h, float s, float v ) {
/* modified from Alvy Ray Smith's site: http://www.alvyray.com/Papers/hsv2rgb.htm */
// H is given on [0, 6]. S and V are given on [0, 1].
// RGB is returned as a 24-bit long #rrggbb
int i;
float m, n, f;
// not very elegant way of dealing with out of range: return black
if ((s<0.0) || (s>1.0) || (v<0.0) || (v>1.0)) {
return 0L;
}
if ((h < 0.0) || (h > 6.0)) {
return long( v * 255 ) + long( v * 255 ) * 256 + long( v * 255 ) * 65536;
}
i = floor(h);
f = h - i;
if ( !(i&1) ) {
f = 1 - f; // if i is even
}
m = v * (1 - s);
n = v * (1 - s * f);
switch (i) {
case 6:
case 0:
return long(v * 255 ) * 65536 + long( n * 255 ) * 256 + long( m * 255);
case 1:
return long(n * 255 ) * 65536 + long( v * 255 ) * 256 + long( m * 255);
case 2:
return long(m * 255 ) * 65536 + long( v * 255 ) * 256 + long( n * 255);
case 3:
return long(m * 255 ) * 65536 + long( n * 255 ) * 256 + long( v * 255);
case 4:
return long(n * 255 ) * 65536 + long( m * 255 ) * 256 + long( v * 255);
case 5:
return long(v * 255 ) * 65536 + long( m * 255 ) * 256 + long( n * 255);
}
}
The circuit is very simple:
- Digital pin 9 → 165Ω resistor → LED Red pin
- Digital pin 10 → 100Ω resistor → LED Green pin
- Digital pin 11 → 100Ω resistor → LED Blue pin
- GND → LED common cathode.
The different resistor values are to provide a limited current to the Triple Output LED RGB – Diffused, as each channel has different requirements. The 165Ω resistor is actually two 330Ω in parallel; I didn’t have the right value, and this was the closest I could make with what I had.
dude, you so need your banjo to glow in the dark
what (if anything) were they thinking?
O Canada – as performed by sampled wailing babies.
first LED
Saw my first retail LED domestic bulb today – $14 at Rona. Looked more like a novelty than anything else, but it did have a stated 100,000 hour life…
this is not graph paper
The PhotoSmart has an ability to print various ruled paper forms: lined, todo lists, and graph paper. But what they print for graph paper is merely squared paper:
Graph paper’s the stuff with 1mm squares. Personally, I was disappointed that it wouldn’t print log ruled and Smith charts, but that’s just me …
prescient Upton
One of the baddies in Upton Sinclair’s The Jungle is a political henchman called Bush Harper. No further comment is required.
All the printers I’ve ever owned …
- An ancient (even in 1985) Centronics serial dot-matrix printer that we never got working with the CPC464. The print head was driven along a rack, and when it hit the right margin, an idler gear was wedged in place, forcing the carriage to return. Crude, noisy but effective.
- Amstrad DMP-2000. Plasticky but remarkably good 9-pin printer. Had an open-loop ribbon that we used to re-ink with thick oily endorsing ink until the ribbons wore through.
- NEC Pinwriter P20. A potentially lovely 24-pin printer ruined by a design flaw. Print head pins would get caught in the ribbon, and snap off. It didn’t help that the dealer that sold it to me wouldn’t refund my money, and required gentle persuasion from a lawyer to do so.
- Kodak-Diconix 300 inkjet printer. I got this to review for Amiga Computing, and the dealer never wanted it back. It used HP ThinkJet print gear which used tiny cartridges that sucked ink like no tomorrow; you could hear the droplets hit the page.
- HP DeskJet 500. I got this for my MSc thesis. Approximately the shape of Torness nuclear power station (and only slightly smaller), last I heard it was still running.
- Canon BJ 200. A little mono inkjet printer that ran to 360dpi, or 720 if you had all the time in the world and an unlimited ink budget.
- Epson Stylus Colour. My first colour printer. It definitely couldn’t print photos very well.
- HP LaserJet II. Big, heavy, slow, and crackling with ozone, this was retired from Glasgow University. Made the lights dim when it started to print. Came with a clone PostScript cartridge that turned it into the world’s second-slowest PS printer. We did all our Canadian visa paperwork on it.
- Epson Stylus C80. This one could print photos tolerably well, but the cartridges dried out quickly, runing the quality and making it expensive to run.
- Okidata OL-410e PS. The world’s slowest PostScript printer. Sold by someone on tortech who should’ve known better (and bought by someone who also should’ve known better), this printer jams on every sheet fed into it due to a damaged paper path. Unusually, it uses an LED imaging system instead of laser xerography, and has a weird open-hopper toner system that makes transporting a part-used print cartridge a hazard.
- HP LaserJet 4M Plus. With its duplexer and extra paper tray it’s huge and heavy, but it still produces crisp pages after nearly 1,000,000 page impressions. I actually have two of these; one was bought for $99 refurbished, and the other (which doesn’t print nearly so well) was got on eBay for $45, including duplexer and 500-sheet tray. Combining the two (and judiciously adding a bunch of RAM) has given me a monster network printer which lets you know it’s running by dimming the lights from here to Etobicoke.
- IBM Wheelwriter typewriter/ daisywheel printer. I’ve only ever produced a couple of pages on this, but this is the ultimate letter-quality printer. It also sounds like someone slowly machine-gunning the neighbourhood, so mostly lives under wraps.
- HP PhotoSmart C5180. It’s a network photo printer/scanner that I bought yesterday. Really does print indistinguishably from photos, and prints direct from memory cards. When first installed, makes an amusing array of howls, boinks, squeals, beeps and sproings as it primes the print heads.
but what can it *mean*?
GO train tickets say: “Ticket must be cancelled to be valid.” Wha?
the great lost opportunity
I’ve always thought that Adobe missed a great opportunity when they didn’t make their basic PDF writer freely available for Windows. Other OSs now have transparent print-to-PDF options. If you’re lucky, a corporate PC might have MS Office Document Image Writer installed, but a 300dpi monochrome TIFF can’t compare to a PDF.
Still, one can always install PDFCreator (if you have admin rights to the PC, of course). It’s a shame they decide to bundle a marginally dodgy toolbar/spyware package with it, but you don’t get that if you use the MSI installer package.
providing cannon fodder for empire since 1867
I reckon that if I took a random street poll anywhere (anywhere outside Canada, that is), no more than 3 out of 10 people would consider Canada as having a leadership role. I do not wish to make light of the soldiers’ plight; I just don’t want them there in my name.
(I was going to make a comment about the nearest thing to a role to most Canadians would be a Swiss Chalet 1/4 chicken dinner, but that doesn’t work in a written context, and barely works when spoken.)
a tiny stub-tailed birdlet
Our tree is filled with Ruby-crowned Kinglets, and the title is Peterson’s poetic description of them. I guess they’re feeding up to migrate a bit south. Give news of yourselves when you bring spring back with you!
amalgam squidge
Got yet more mercury alloy trowelled into my head tonight by Dr Choi. I have to say, the best bit about going to the dentist is the squidgy noise the filling paste makes as it compresses into the cavity. It means it’s nearly over, and the burring slow drill is banished until next time.
not the smartest loaches in the tank
Came home, said hello to the fish, and did a quick count; I was one loach down, and the CO2 generator had an orange tail …
Seems that one of the loaches had decided it was way cool to get wedged up the back of the gas generator, and couldn’t get back out. I gingerly pulled off the device from the side of the tank, and the loach fluttered off, a little dazed.
No sooner had I put the generator back did another loach zoom up and get jammed. It must’ve been told that you got a “wicked headrush, dude”.
And for this reason, loaches don’t rule the earth.
Goodbye, childhood
Goodbye:
- headache glue cracking from finger tips
- badly-painted pilot with obvious thumb-prints
- squint and/or torn decals
- undercarriage installed backwards, if at all
- spilled tin of Humbrol enamel
- leftover sprue rattling in cardboard box with an unidentified piece still attached
- curious v-shaped stand that never quite stood level
- hung squintly from bedroom light by white thread until dusty wing missing from too many runins with parental heads
- taken down for final flight whirled round head on string until dashed against clothespole or arcing up up into neighbour’s fir tree (it’s still there today)
- when older, packed with cotton balls nicked from sister, doused with turps, crashed flaming kamikaze onto the compost heap (sorry dad, your onions never did well on paint thinner and burnt plastic)