Friday, December 2, 2011

Gakken Kit #32, the Mini Denchi Block

Gakken has been moving steadily into the electronics realm over the last 1-2 years, starting with the DC motor car, then the theremin, Poulson recorder, guitar and the Japanino. Kit #32, the latest one out, is the first real step into electronics design. With the previous kits, the electronics concepts were still masked by the surface application (i.e. - producing music, or writing software). But, the 25 block mini Denshi kit actually requires you to learn how transistors work and to calculate current flow in order to avoid blowing out the more sensitive parts.

Kit #32, Mini Denshi Block, released Nov. 30, 2011, 4000 yen ($50 USD).
Includes suggestions for 50 different experiments.

(The kit is about 4" x 6". Shown here with the earphone, microphone cup, and two jumper wires (used as contacts, sensors, switch plates and jumpers.) You can remove the ear piece from the earphone and replace it with the cup to turn the earphone into a microphone for the amplifier speaker and PA circuits. The decal at the top left corner refers to the wiring of the contacts running along the left side of the case. Primarily, the left side contacts are for the radio tuning coil.)

The mini Denshi ("electronics") set is a scaled-down version of the EX-150, but the principles are the same. You start out with a plastic holding case, and 25 plastic cubes. Each cube contains one part - a wire, resistor, transistor, diode, LED, capacitor, etc. The holding case has fingers at the bottom to allow you to snap in each of the components as you like. Contacts on the inside of the case touch the contacts on the sides of the cubes to form the circuit. The holding case also contains the battery pack (3 AAA's), a power switch, an adjustable coil and a speaker. Actually, building the suggested circuits is pretty simple, since the cubes are all clearly marked and you just have to follow the pictures. The case itself requires assembly (mounting the speaker, switch, decals, battery holder, etc. The suggested time is 20 minutes, and it took me about 15. The main challenge is in routing the wires to avoid having them float or get pinched.) If you want to have a bottom cover over the wires and circuit board, you're encouraged to punch out the plate from the main box and stick it in place using double-sided tape. I didn't bother with it because the plate is just cheap cardboard.

(Back view. Cardboard backplate not included. You can see the speaker, speaker driver board, batteries, and radio tuning coil at the top of the case.)

Now, as for the theory behind the kit... Well, I went to a technical school for 2 years for an associate's degree, and then a university for another 4 to get my BSEE. This is not something you'll pick up after reading a blog entry for 5 minutes. Suffice it to say that you can get some information from wikipedia, and the Gakken site will probably have English instructions by the time the kit makes its way to the U.S.

Some highlights - current flows from positive to negative. By convention, "ground" is 0V. With the 3 AAA batteries, the power pin will be around +4.5V. It doesn't take much to destroy a transistor or a diode, so if you don't know what you're doing, just be real sure to closely follow the pictures in the mook.

There is a relationship between voltage, current and resistance. It's called Ohm's Law, and it looks like:
Voltage = current * resistance. or,
V = I * R

If you have a 10 milliamp fuse, you need at least:
R = 4.5V / 0.01A = a 450 ohm resistor or bigger

in series (in line) with the fuse to avoid burning it out. Since LEDs are like 40 or 50 mA fuses, you should put a 220 ohm resistor in series with an LED to protect it as a general rule. Fortunately, the 2 LED blocks (1 red LED, the other green) both have the resistors already wired in for you.

If a diode, LED or transistor is damaged, it usually dies right there. If it's dead, forget about the circuit working any more. So, BE CAREFUL.

It's hard to draw an electrical circuit to look like something in the real world. Instead, we use special symbols to represent the individual components of a circuit. The total circuit picture is called a "schematic diagram" (or "circuit schematic"). When you look at the cubes of the kit, you'll see these schematic symbols stenciled on the top of each one.

Another thing to keep in mind is that the direction of the component matters for diodes, LEDs and transistors. If you put the part in backwards, the circuit won't work. You may not damage the component, but the thing you're trying to build won't do anything, or, at least, won't do it right. Additionally, certain kinds of capacitors do care which direction they're facing, and can suffer physical damage if plugged in the wrong way. So, again, be sure to have the blocks in the circuit look exactly like they are in the pictures in the mook.

Regarding the mook - it's 124 pages this time, roughly 2/3's of which is dedicated to the assembly of the kit, and the descriptions of the 50 circuits you can build. There's another 6 circuits identified as "Denchi mini 120%", which can only be built if you have 2 kits. Many of the circuits are kind of silly, such as making variations on the "turn on the LED with 1, 2, or 3 switches" - these are essentially the same circuit but using extra wires. Some of the circuits attempt to teach how AND, NOR and XOR gates work, but again, it's just one transistor with different switch wiring configurations. The Lie Detector and the Love Compatibility circuits are also very similar. Probably the more interesting projects are the crystal radio with 1-transistor amplifier, and the analog synthesizer. If you've got 2 kits, then you can make the 4-transistor radio.

Articles in the mook include artistic photos of old circuit boards (including a Korg 800DV synth, and a Hitac-10 mainframe computer), art projects using the denchi blocks to make running figures, a story on the history of the denchi block product dating back to 1966, and a study in optical illusions and how the wiring of the human eye and brain allow illusions to work. No real theory of electronics, history of the science, or biographies of the scientists involved in it this time. The manga at the back of the mook talks about animal sex.

Suggestions for modding the kit include: putting it in a rabbit pouch to turn it into a purse; driving LEDs to make an illuminated photo of the Big Dipper; driving larger circuits for a synth and a rhythm box; making a Geiger counter; and wiring up to a Japanino to make an LED bar volume level display. I would argue that if you're going to build the rest of the support circuitry for a Geiger counter, that there's no real need to put the denchi block kit in the circuit because it's so bulky compared to the rest of the assembly. But, if you have the denchi block kit, I guess you're going to want to make the most use of it.

The kit works fine for making the various suggested circuits, and it is very well-constructed. The spring contacts do push the blocks apart a bit so you'll need to keep pushing them down into place as you assemble the experiment to ensure electrical contact. But, on the whole it is a good introduction to simple electronic design, without requiring the use of solder and an iron. Meaning that it's good for kids to play with. My only complaint is that there's no direct source for cheap blank blocks for adding in more components later (I'd like some more capacitors, other colors of LEDs, and at least one trim pot.) That, and if you get this as an import it's going to be at least $65 USD, which places it on the low side of the bang for the buck scale. It would have been nice to have this kit when I was in tech school.


Next up, #33. The desktop robot vacuum. Tentatively scheduled for the second half of January, 2012.


TSOTE said...

Kit #32 came out just before my Japanese language proficiency test on Dec. 4th, so I held off on really trying to build any of the circuits until after the test was over. Initially, I just wanted to find the fun circuits, but I started translating the experiment names from Japanese, and ended up going through each of them one at a time, adding comments and explanations. About halfway through, I discovered that 1 of the two transistors wasn't working. I'm not sure if I blew it out, or if it had never worked. It kind of looks like there's a cold solder joint, but I haven't found a place selling soldering irons in Kagoshima. If it is blown, then I need to get a replacement block from Gakken, and I've never had to write to them for something like this before. Don't know how long it'll take (or how much) for a replacement. Most of the remaining circuits use both transistors, so I don't have much choice but to wait.

Synthed Mind said...

I just bought this little marvel of electronics. The manual, which comes with it, shows lots of pictures of the Gakken EX kits through the years. Right now, I'm busy translating the kit manual and so far, I've already done the assembly instructions. You can find it here :
Later on, I will add even more experiments and explanations of the circuits. Just keep hanging on and post a little message if you would like it.