Do you like to build electronics kits, but wish that more of them came with step-by-step instructions and pictures?
No? Then, um, don’t read this article. Do you like cats, but wish that more of them made amusing, oddly spelled comments? Look at this!
As for electronics kits, it’s a shame that the most widely-distributed line of kits come with just Ikea-like pictograms for instructions, and don’t even try to teach you anything about the design of the electronic circuit. Some kits, like those from Adafruit and Evil Mad Scientist Labs, get the balance just right, providing instructions that are easy to follow and educational. Many of the best kits, though, are skimpy on the assembly details.
The kit designers are, I imagine, old hands at electronics who can solder components together as effortlessly as a kid building something out of Lego. Things are not so intuitive to beginners, though, and even experienced kit builders will sometimes be thrown off by misleading labels on a circuit board, or 2 seemingly identical components that aren’t actually interchangeable.
So, I thought it might be useful to someone to post step-by-step assembly descriptions of kits that I build. I also like the idea of giving my blog’s admittedly modest exposure to kits that I admire and think others might enjoy building too.
First up, kitsrus‘s K134: Introduction to LCDs.
I’m a big fan of kitsrus. Their kits tend to be geniuinely useful electronic devices, with some flexibility in how they are powered, connected to their input and output devices, and adjusted for performance. They also include quite detailed descriptions of the design of the circuits. I’ve yet to be disappointed with one of their kits.
Kit 134 is, at first glance, somewhat outdated since it drives the LCD from a parallel port rather than a USB port or a microcontroller. However, since parallel connections to LCDs are the cheapest and simplest to understand, the theory behind the circuit is well worth learning. In addition to the relatively detailed instruction sheets included with all kitsrus kits (and also available as a PDF on their web site), kitsrus has also made available a more detailed technical writeup from an electronics magazine, Silicon Chip, and the datasheet for the somewhat obscure LCD model. Providing the datasheet is the kind of gesture that I really appreciate from kitsrus — most kit vendors don’t even bother to give you the manufacturer’s part number.
As mentioned later in this artcle, I was also somewhat surprised to find a recent piece of open source .Net software that is, by a happy coincidence, compatible with the kit, breathing new life into it. All things considered, this kit is an excellent educational project as well as a useful platform for additional experimentation.
Like all of kitsrus’s kits, K134′s circuit board, shown below, is well laid out. All of the parts are clearly labeled, the circuit connections on the back of the board are clear to the eye , and there is a reasonable amount of space between components, making the soldering less frustrating for beginners.
As with any kit, it’s a good idea to start with the smallest components. Resistors are the salad of kits building – a nice warmup to the main course. In this case, all 4 resistors are exactly the same, 1K, so it’s hard to go wrong.
Next up are the diodes. Unlike the resistors, these have polarity, so they must be positioned as shown. The gray stripe on the left of the 1N4004 is obvious, but I remember being somewhat unsure when I first started building kits about whether that blank mark on the Zener diode was the stripe. It is, so make sure that it is facing towards the top of the board, as shown in the photo below.
Diodes - right side up!
Incidentally, the thick leads on the 1N4004 diode make them a little tougher to solder, so don’t be shy about holding the solder iron next to the lead until the solder starts to flow. As far as I know, it’s pretty much impossible to overheat one of those suckers — taking the heat is their job, after all.
There are 3 different capacitors in this kit. The beige tantalum capacitor can go in either way, but the black electrolytic capacitors, like the diodes, have polarity. The white stripes of these 2 capacitors must face towards the bottom of the board, as shown in the photo below. This side of the capacitor, the negative, is also indicated by a shorter lead.
Electrolytic capacitors even have their size printed right on the side – 10 uF and 100 uF. Such a helpful young component! Unlike that stupid little tantalum capacitor. 104, you say? Yeah, right, good to know.
The potentiometer is up next. This part of the assembly is a little tricky because the kit appears to have been designed to handle 2 different sizes of potentiometers. As a result, there are 2 different circles with 2 different pin positions on the circuit board. My kit came with a smaller potentiometer, so the hole at the right of the larger circle is unused.
The potentiometer is also the first component in this build to have a gravity problem — when you flip the board over to solder the potentiometer’s leads, you’re likely to find that it pops out. Most kit instructions, when they bother to mention this type of problem at all, will tell you to hold down the component with a finger while you solder. Personally, I think that’s bad advice. Unless you’re an experienced kit builder or an orangutan, you’re likely to find that this results in a) a clumsy solder joint, b) a burnt finger and/or c) a lopsided component.
Take it from me, there is no shame in using masking tape to hold down the component. While the tape will leave a slight bit of adhesive residue, I’ve yet to have that affect a kit. I have, on the other hand, found that clumsy solder joints and burnt fingers have a considerable effect on the kit and my piece of mind.
If soldering the potentiometer didn’t convince you of the merits of masking tape, the 5-pin connector at the top of the board might do the trick. Even veteran solderers are hard-pressed to get these connectors in straight. A guy working at SparkFun recently wrote about a clever solution to this problem — slightly offsetting every other hole so that friction holds the connector in place — but his idea won’t help you here.
Note that the small pins on the connector face down, into the board. Don’t worry if your connector ends up crooked, or even if it is more seriously maimed, since you probably won’t be using this connector anyway. It is used to optionally connect the thermostat chip on the board to another project — for example, if you had a heater that you wanted to control with this kit. For the purpose of learning to program an LCD you can safely ignore the 5-pin connector.
Next up is the mysterious “link” connector. There isn’t a separate part in the kit for this: you can just use the lead clipped from one of the other parts, such a a resistor. Just fold the two ends down to form a staple-like shape, insert it into the board, and solder the two ends to underside of the board. I have no idea what the purpose of this part is. I’d suspect it was used to correct an error in the circuit board if there wasn’t a silkscreened “LINK” label on the board. If you can set me straight on the purpose of this part of the design, please add a comment below.
It’s time for one of the bigger components, the DC power jack. This is another instance where a strip of masking tape might come in handy. This is the first component in this build where the solder needs to do more than make an electrical connection – it also needs to hold the DC connector in place. Unlike most of the components on the board, the DC connector will pushed and pulled as you use the board, and the only thing that will keep it in place is a big blob of solder. So, as shown in the image below, you’ll want to be generous with the solder for each of the 3 blades of the plug.
Incidentally, the blade that is at right-angles to the other 2 isn’t actually part of the circuit – you can see that on the underside of the board, since the circuit etchings don’t touch that connector. That part is there simply for ballast, so be sure to smother it in solder. Also incidentally, the orientation of the other 2 blades is what determines whether the tip is negative or positive. In this case it is positive, as noted on the circuit board, so if make sure that you use an AC adapter that has a positive tip. If the board designer had switched the circuit connections to the blades of the power jack, then it would be a negative tip. If you’re laying out your own circuit on a breadboard or prototype board you get to match the jack to the adapter type that you want to use, but in this case you’re stuck with a positive tip.
Next up is the thermometer chip. More correctly, this is a combination thermometer and thermostat, a Dallas Semiconductor DS1620. You can get the full datasheet for this chip from the kitsrus web site, if you’re interested. While you could just solder chips like this directly to the circuit board, using a chip socket has 2 advantages — you can reuse the chip on another circuit, and the heat from the soldering iron won’t damage the chip. In this case, both the socket and chip were embedded in styrofoam, as shown on the right.
Remove the socket and place it onto board, below the 5-pin connector. As shown below in the photo to the lower left, the notch on the socket should face left, towards the resistors.
You shouldn’t need to press too hard on the socket to get it into place. If you’re finding it difficult to insert, then the problem is likely with one of the socket’s pins being out of place. Make sure that each pin fits into a hole on the circuit board, rather than being bent underneath the socket. It’s possible that one of the pins was bent during shipping despite its styrofoam armour – if the socket doesn’t easily fit into the holes of the circuit board, gently bend the offending pin(s) with your fingers. Try not to wiggle the socket’s pins too much, though, since they can snap off. If that happens, you have 2 choices: buy another socket (they are only a buck or two) or, in this case, leave the chip out of the circuit entirely. As explained later in the follow-on to this article, I found the LCD part of this circuit far more useful than the temperature monitoring, so the chip isn’t a must-have.
Now for the two stars of the show: the parallel port connector and the LCD. Both of these involve a lot of soldering of small pins, so you’ll want to make sure that you keep your soldering iron tip clean and use small amounts of solder. Note the relatively small size of the solder joints in the photo below, compared to the joints seen in other photos. If you drop a huge blob on any of the pins, there’s a chance that you’ll short the connection to the next pin. Since most of the parallel port pins and all of the LCD pins are used in this circuit, shorting 2 pins is almost certainly going to ruin the party.
The parallel port connector needs to be anchored down well, since connecting and disconnecting the heavy parallel port cable head is going to put some strain on it. That’s what the 2 big pins on either end of the circuit board connection are for. Be sure to dump a lot of solder on those 2 suckers.
The LCD is connected to the circuit board using a 16-pin connector. The pin connector actually has 2 parts — male and female — and in my kit they were already connected together. Get a room, you two! You’ll have to pull them apart in order to solder them into the circuit.
As shown on the left, the female connector goes goes on the top of the circuit board (held in place for soldering by my faithful strip of masking tape). The male connector goes on the underside of the LCD. This arrangement is quite handy, since using the pin connectors makes it possible to reuse the LCD in other circuits. Since the LCD uses a standard chipset that is supported by a lot of software, you’ll probably find a lot of other uses for the LCD.
The “standard chipset” part may come as a surprise to you if you Googled the LCD’s manufacturer and model (a defunct MCC162 made by Truly Semiconductor Ltd.). There’s not much information about it on the web. The reusability of the LCD may come as a surprise even if you looked at the spec sheet (which kitsrus helpfully provides on their website, since you aren’t likely to find the MCC162′s specs anywhere else). The spec sheet states that this board uses a Samsung KS0070 chipset, and the industry (and hobbyist) standard is the Hitachi HD44780. However, I came across an intriguing article on The Code Project website which shows how to program a KS0066-based LCD through the parallel port using Microsoft’s .Net Framework. As stated in the article, the KS0066 (and, it appears, the KS0070) are compatible wit the HD44780. This is great news — you’ll be able to use this kit’s LCD with most of the LCD-based projects you find on web sites.
Note that solder which holds the male pins to the LCD actually goes on the top side of the LCD board — having got into the habit of turning the main circuit board upside-down to do the soldering, it’s easy to get mixed up and solder the male connector pins to the wrong side of the LCD board.
This completes the assembly part of the project — sort of. As wisely suggested in the Silicon Chip article about this kit, you should test the voltage being supplied to the temperature chip’s socket before plugging in the chip. This type of precaution is a good idea for any project that involves sensitive semiconductors, but unfortunately many kit makers don’t teach this practice. To test the voltage, plug a positive-tip 12V power supply into the CD jack. Then, as shown in the photo below, set a multimeter to the DC voltage setting and put the negative probe on the socket for pin 4, and the positive probe on the socket for pin 8. (Pins are always numbered counterclockwise, starting from the end of the chip with the notch. So, when the board is oriented as shown in the photo, pin 4 is the bottom right socket, and pin 8 is the upper left). The voltage should show somewhere between 4.9 and 5.1 volts — if not, check your power supply, then check the solder connections in the components between the DC jack and the chip socket for bridges.
When checking the voltage, you can also check that the LCD is working correctly. You should see a series of black rectangles, as shown in the photo. (As mentioned earlier, the LCD works without involving the temperature chip. In order to see something other than black rectangles, though, you will need a PC and some software). If the LCD is blank, you hopefully just need to adjust the contrast. After I assembled the kit I found that the contrast was turned all the way down, so I had to turn the potentiometer clockwise, as shown in the photo below, before the black rectangles appeared.
If the voltage and LCD look fine, then you can unplug the power jack, then insert the temperature chip. These chips generally are shipped with the pins spread a little too far out for the socket, so you’ll need to bend the pins on each side inward by gently pushing them against a table. They should point in just a bit, as shown in the photo below, before they are ready for the socket.
Now you’re ready for the hardest part of this project — finding a parallel port cable. The cable that you need is a parallel port extension — 25 pins female on one end (for the kit) and 25 pins male on the other (for the PC). Back in the day, these were used to extend the distance between the printer and the PC. Note that all 25 pins need to be wired up, unlike a 25-pin serial port cable. As a result, the cable you want is thick - mine is about half an inch. If you found a cable that is thin and cheap, it almost certainly is a serial port cable, and it isn’t going to work with this kit.
Finding a PC with a parallel port may prove to be just as difficult. You may need to purchase an IDE parallel port card just for this project. They aren’t expensive but are somewhat hard to find — this one from DealExtreme worked for me . You may come across a USB-based parallel port connector — unfortunately, that isn’t going to work this kit or any parallel-based electronics project, since the USB driver is intended to work with a printer only.
Having scrounged up an outdated parallel port and cable, it’s time to deal with the outdated software. When this kit was originally released back in 2000, it came with DOS-based software. This software works fine with Windows Me and earlier, but Windows XP rendered it obsolete, since XP doesn’t let DOS programs interface directly with the parallel port. Fortunately, the kitsrus website now provides a Windows version of the software, which comes with a DLL that is needed to communicate with the parallel port. This software is intended for Windows XP, but I found that it worked on Windows Vista too if you run it as an Administrator (that is, right-click on the .exe and select “Run as administrator” from the pop-up menu).
If all of that went well, you should find some scrolling text on the LCD. Switch the software over to Temperature mode, and you should see a display like the one below.
Finding out the temperature in your computer room (rounded to the nearest half degree, actually) may seem a little anticlimactic considering the amount of work needed to get this puppy to run. However, this project has 2 big advantages over your average electronics kit. Firstly, the excellent Silicon Chip magazine article will explain how it works, something which few kit makers share with their customers. Secondly, the fact that the kit uses a standard interface (the parallel port) and a standard LCD chipset (HD44780-compatible) means that you can use this kit with other software that you’ll find on the web. I’ll explore one such program in the follow-on to this article