07 June 2016

A clock with Arduino and four HP 5082-7300 displays - 3

Last part in this series about building a clock with four HP 5082-7300 displays controlled with an Arduino.
After using the HP 5082-7300 desk clock for a whole day and night I came up with few improvements.
First of all, during the day nobody will look at it; why keeping it running, then? The are many ways to control it via software, like switching off the display according to the time of the day, to the room brightness, to a physical presence and you can certainly come up with other ideas. Instead of developing a software solution I will add a switch to control DC power to the whole circuit.
Meanwhile I wrote and applied some firmware updates. The first refinement is meant to reduce heat production, which occurs during the day when nobody looks at the clock: cut in half the display brightness at the higher luminosity levels. It does have an effect since the top of the box is not warm anymore. Then, since every digit has the decimal point, the new firmware moves around the dot endlessly instead of just blinking the central one. Third and last change was to read the LDR value once a second instead of once every PWM loop: this makes the loop a bit faster (ca. 0.1 ms) thus reduces flicker.
A further improvement could be to add some hysteresis and averaging to the intensity control, not counting adding further digits.

The firmware is available on github. Homework: are there other functions I have not described in these three posts?

05 June 2016

A clock with Arduino and four HP 5082-7300 displays - 2

Part two of how I designed and built my own bedside clock with a 1970's touch.

The finished clock, in the operating position.
This time my adventure started from the enclosure: a wooden box with the top cover almost completely transparent I had bought to use with a VFD clock but turned out to be too tight for it. Inside there is enough room to fit the whole circuit and ensure air flow for heat transfer (remember an HP 5082-7300 dissipates 500 mW on average!).

I have read online that these displays fail mainly because of overheating or stress from prolonged heat. I do have few spares but I really care to do my homework properly!

Therefore I cut a piece of perfboard to the desired size and started planning the layout: displays would be on the upper-right corner and the rest underneath. I decided that everything should be visible through the glass window (except for wiring) so that it would be easier to describe the clock to friends visiting my place (in that case the box will be moved to a more visible spot, like the kitchen furniture). Nevertheless I tried to keep a clean wiring scheme, pleasant to be seen.

Since these displays have a Latch Enable line, they keep displaying the digit once it has been loaded into their internal buffer. In order to drive these displays I need:
  • 4 lines for the 8421 BCD code
  • 1 line for the decimal point
  • 1 line for each display (4)
Lid open.
So it is 9 lines going from the Arduino-like to displays. Instead of running them through the board I used a set of pin headers just in case one day I will decide to separate logic from display areas. This holds true for +V and GND as well. The effect is a bunch of colored wires connecting two areas of the single board: they add a touch of color :-)

The RTC board is a cheap battery-backed DS1302 I2C module that appears to be pretty stable. I added an LDR to do brightness control (ADC in microcontroller and PWM control on displays) and made provision for two pushbuttons that help setting the time.

As microcontroller board I chose a clone of Arduino Nano v3, because it is small and still has a strong USB socket for firmware updates.

Given the power requirement of HP 5082-7300 displays I need an external PSU, but since I want to run the whole thing at 4.2 V, I had to add a further switching step-down module inside (on the back of the perfboard).

Isn't display brightness affected with the lower supply voltage, you may ask? It is indeed, they look dimmer (and dissipate much less power!), but I will look at this clock at night in a dark room, so that's what I am looking for afterwards! The voltage can be even lower, but then brighness is not even anymore.

And after running it for 24h I came up with few firmware adjustments, covered in the next article of this series.

03 June 2016

A clock with Arduino and four HP 5082-7300 displays - 1

I needed a time display on my bedside table and I wanted it with an electronic vintage touch. So I gathered:
  • 4x HP 5082-7300 displays
  • an Arduino-like board
  • an RTC module
  • a perfboard
  • some female pin headers
  • wire, solder, tools, ...
  • a 5 Vdc source
  • an LDR
  • a couple of N.O. pushbuttons
Four HP 5082-7300 displays.
An HP 5082-7300 display is an early LED display developed before 7-segments became the de-facto standard. It includes a BCD decoder and it displays 0-9, dash and blank and a right hand side decimal point. Each segment is composed of few LED dots, so it mimicks a dot-matrix display. It works from about 4 V to 5.5 V and it drains an average of 100 mA at 5 V: that's half a Watt per display! We are talking about late 1970's technology.

So, why using these power hungry displays in 2016? Simple: to learn something new and to save old technology from the recycle bin. Moreover a modern microcontroller makes it very easy to produce a BCD sequence that represents the time of the day.

26 May 2016

Visible + IR sensitive webcam - DIY

A colleague showed up with a thermal camera that attaches to an iOS or Android device. Cost: about 250 USD@2016. His show revived me the interest in trying to remove the IR filter from a (web)camera and see what happens.

I got hold of an old (2004) Creative webcam that works only on WinXP. It is easy to open them up. Not so easy to remove the IR filter: in my attempt I broke the IR filter glass and removed its pieces. The Net is full of tutorials and videos on how to do it, so do your homework and take your time (and wear protective glasses the least!).

Now the camera captures both visible and infrared light. Neat, but not so useful, because you keep getting what looks like over-exposed images with wrong colors.

How to filter the visible spectrum of light? One suggestion online is to use a piece of floppy disk (the magnetic disk inside the plastic, of course). Tried it. Not sure it filters out visible light or it acts as an ND filter (see ND filters in photography). Fail.

A second test was to use the modified camera at night, without any filter. It might work on passing cars, but its frame rate is so slow that cars are just a glob of light caused by long exposure. Fail.

I haven't tried to cover the lens with an old photographic film, the fully exposed frame which is dark. Maybe something will come up.

In any case I think the webcam sensitivity is too low to detect temperature variations at "human" levels, like heat/cold areas of a laptop or an electronic circuit, which would be my main usage at the present time.

23 April 2016

Trying to fix a Copal 602 flip palette

While everything seems to (still) work, inside the Copal 602 clock I found a loose palette. It has one hook missing, and it should be possible to rebuild it with a tiny cut of hard plastic of the proper thickness. I still have to figure out how to keep it in place while the superglue does it job.

But, what if it doesn't work? (Or I get it totally wrong.) I think modern technology can come to the rescue: laser cut. Probably the hardest part to find is the right plastic (let alone the color), then with a 1200 dpi scan of an original palette and a digital ruler on the picture, a digital model can be drawn. Finally it is a matter of few seconds under the laser.

Here is the 1200 dpi scan if anyone needs it.

20 April 2016

Copal 602 flip clock

3/4 side view.
Before LEDs, how were digital clocks made? Not with Nixies, that (in my opinion) were mainly used in instruments where the information to be displayed was more randomic than sequential. There existed flip clocks! It looks like they were invented in Italy.

But at a flea market I found a Japanese production, the Copal 602. It was being sold as an ornament at the cost of few espresso coffees (or one basic fast-food menu, burger + chips + drink): well worth a try, and in any case a curious ornament or case for other projects.

With my surprise the clock does work even though it appears to be running a bit fast, like 40-50 seconds gain per hour. It is very silent, much more silent than a classic clock, and it even has a neon bulb that gently lights up the time (and it works too!).

Copal 602 front view.
Time to have a look inside, since I have no real idea how it works.

14 April 2016

Lucky battery pack

Inside A1060
I've had a battery pack from a MAC PowerBook G4 sitting around for a while. The A1060 pack is rated at 10.8V and probably 4400 mAh. It has charge/discharge protection circuitry and an embedded 5-LED charge status on-demand display. When I took apart the PowerBook I kept the battery connector (board), and that was a smart move.

Needing some 18650 cells, I decided to rescue them from the A1060. I was lucky because the pack was apparently made with servicing in mind, and since the glue has dried over time I could pry it open very easily. This fact immediately changed my plan: check the pack before taking out individual cells!

Now it was much easier to determine the polarity of the battery connector, and therefore of the matching board. In less than ten minutes I was recharging the battery pack at circa 11V 2A input.

Fast forward few hours, the pack stopped charging and the onboard LEDs report 5/5 charge status. I am now monitoring the self-discharge while I plan an endurance test.

Full pack and the matching board inside G4 12"