Gakken EX-System
The Gakken EX-System is a series of educational electronics kits produced by Gakken in the late 1970s. The kits use denshi blocks (also known as electronic blocks) to allow electronics experiments to be performed easily and safely. Over 25 years after its original release, one of the main kits from the series was reissued in Japan in 2002. History
A brief timeline:
 1972 Gakken and Denshi Block Mfg. Co. Ltd. collaborate to release denshi block kits under Gakken's name. 1976 The EX series was released. 1981 The successor to the EX series, the FX series, is released. 1986 Gakken stops producing denshi block kits. 2002 The EX-150 is reissued in Japan, and is successful enough to justify the production of an expansion kit. 2011 Gakken releases a small kit compatible with the EX-system, #32 in their "Otona no Kagaku" mook series. EX-System kits

An EX-System kit consists of:
 a selection of denshi blocks,
 the main unit in which circuits are built,
 some additional external apparatus, and
 an instruction booklet. Denshi blocks

A denshi block (or electronic block) is a small plastic box containing an electronic component. Each block has conductive metal strips on its sides, and when two blocks are placed side-by-side, their metal strips touch allowing electricity to flow between them. The top of each block is labelled with a schematic representation of the component it contains. A circuit is built by placing a configuration of denshi blocks in a two dimensional grid. Because of the two dimensional layout and the labels on the blocks, a configuration of blocks resembles a schematic of the circuit. While most denshi blocks are of a standard size, there are some larger blocks for containing complex components. In particular, the synthesiser block and the FM tuner block are much larger, occupying an area 4x5 standard blocks and 3x6 standard blocks, respectively. The main unit
The main unit holds the grid of blocks (it has room for 6×8 standard blocks), batteries and some additional circuitry. When fully expanded, the main unit contains:
 an antenna circuit, with tuning knob
 an amplifier, with volume control
 a light sensitive resistor (CdS cell / Cadmium cell)
 an analogue meter

External apparatus
Some circuits require apparatus which are unsuitable for putting inside blocks, for example, a crystal earpiece. These have wires which terminate in flat metal contacts, and they are connected to the circuit by sliding the contacts between the metal strips of two neighbouring blocks. Some experiments also involve non-electrical apparatus, for example, the optical fibres from the optical experiments kit. The optical fibres are connected via a special block. Instruction booklet
The instruction booklet gives the correct arrangement of blocks to make each circuit, a full schematic for it and a brief explanation of how the experiment works. The original EX-System kits
The names of the original kits, EX-15, EX-30, etc., give the number of experiments that could be performed with them. By purchasing expansion kits, EX-A, EX-B, etc., any of the kits could be upgraded to support the complete set of 191 experiments. Each expansion kit added new denshi blocks and came with a piece of external apparatus or some circuitry to be installed in the main unit. Note that the EX-FM kit is compatible with all of the main kits, although some of its experiments require blocks from later kits in the series. The reissue kits
The reissued EX-150 kit from 2002 is almost identical to the original EX-150 from the 1970s. Due to differences in the availability of certain components, there are changes in some of the circuitry. A consequence is that some of the experiments have been altered. Optical expansion kit
The reissued EX-150 sold well enough to justify an expansion kit. It is designed for the reissued EX-150 only and, allegedly, will not work with the original. The expansion contains components for performing optical experiments, including LED blocks, optical fibres and a 555 timer IC block. As some of the experiments involve two separate circuits, a plastic tray with room for 6 x 5 standard blocks is also provided. An example experiment:
 The kit includes a disk with bands of black and white regions printed on it. The user builds a circuit in the tray which spins the disk. In the main unit, the user builds a circuit which can "read" the regions via the optic fibre and produce a sound. By moving the end of the optical fibre across the spinning disk, the user can play notes of the musical scale. Trivia

The sound synthesiser was based around the Texas Instruments SN76477 sound chip. Since the chip requires a separate 9V power supply, the synthesiser block had a compartment for holding a 9V battery. Although the EX-FM tuner block supported 10 new experiments in Japan, in
the English language version available in Europe, only 4 experiments are described. A Japanese man, Hiroyuki Inoue, built an IPv6 communication module as a block for the EX-150. The Denshi Block system was also sold under the Humbrol, Skilcraft  and Tron Link brands. FX-System

The FX-System was introduced in 1981. It used TMS1000 processor. References

Dostál, J. Electronic kits in education. Olomouc, EU: Votobia, 2008. 74 s. . External links
 Gakken's EX-150 Page
 Denshi Block Mfg. Co. Ltd. Home Page
 A Flickr photostream of the EX-150

Products introduced in 1976
1970s toys
1980s toys
2000s toys
2010s toys
Educational toys