Speak & Spell History
The Speak & Spell goes back to the late 1970s at Texas Instruments. A team of engineers led by Paul Breedlove started with a budget of $25,000 and were tasked to look into speech synthesis. The result of their research was the world’s first single-chip voice synthesizer (the TMC0280) which used a 10th order linear predictive coding model using a pipelined DSP core.
The speech synthesis data needed to generate the spoken words was originally stored on two 128Kbit metal gate PMOS ROMs (incidentally, this was the largest ROM in commercial use at the time). The original spoken data was captured and processed on a minicomputer that was larger than a PC, smaller than a mainframe. Errors were removed and the data was compressed so that the voice data was streamed at 1000 bits per second.
But the Speak & Spell was not just the first electronic spoken single chip solution—it was also one of the earliest handheld game systems. To be more specific, it was one of the first systems that integrated power, controller, and display all in one unit. It was also one of the first systems to use interchangeable cartridges that could expand the system to run different programs.
The Speak & Spell went through various models with its production run ending in 1992. In this teardown, we will look at one of the last production runs of the Speak & Spell called the “Super Speak & Spell”.
Main Front Cover
The front of the Speak & Spell shows a 16 x 2 LCD, a full QWERTY keyboard, a speaker, and the function keys needed to select menu options.
The button action uses a membrane system similar to the ZX80 and can only be described as being horrible to use. There is a fantastic quote for this type of keyboard action that is from the BBC docudrama “Micro Men”, a film is about the home computer market competition between Acorn and Sinclair. At one point Steve Furber from Acorn says this about the ZX80 keyboard:
“Its like trying to read brail through gardening gloves”
The front of the Speak & Spell
The side of the Speak & Spell shows a 3.5mm headphone jack (no doubt for irritated parents as the device sounded like a bad 80s robot with every button press).
The side of the Speak & Spell
For those interested, the serial numbers and other production numbers
Getting the Speak & Spell open only requires two screws, but there is a catch! They are the star head variety, which I luckily have a set in the workshop. With these two undone, the back pops off, revealing the internal workings of the toy.
Inside the Speak & Spell
Darn star screws!
You can see from the photo that the unit takes four C-size batteries and has an expansion port next to the battery compartment. This Speak & Spell came with Expansion Module No 1, which contains additional programs for the Speak & Spell.
This module is slotted in using an edge connector and is easily removed
The front keyboard is connected to the main PCB via an edge connector that connects to a ribbon cable. This cable has traces made of carbon (which is identical to the ZX Spectrum keyboard connection method) and is easily broken, so always be careful with these!
Carbon keyboard cable
PCB and ICs
The main PCB is fitted in with just one screw and is easily removed. Only three main ICs are on the PCB and one of these (the LCD controller) is a surface mount part. This comes to no surprise considering this toy is from 1992.
The main PCB
The first IC is CSM42030BN2 and is a custom TI part. This IC is the DSP (Digital Signal Processor) of the Speak & Spell and is responsible for the speech synthesis, keyboard control, and other microcontroller functions. No parts here are socketed!
The Speak & Spell DSP IC
The second IC is the CMM19048N which, again, is a custom TI part. Online resources indicated that this is the main ROM for the system that holds data and basic software.
The main ROM of the system
The third IC is the HDD4780, which is one of the most popular hobby components (arguably) as it is found in just about every Alphanumeric LCD. Why is such a chip so popular among professionals and hobbyists alike these days? The answer is rather simple: don’t fix what ain't broke! So many applications (commercial, industrial, etc.) use LCD displays and this chip provides a fantastic system to send ASCII-encoded data.
HD44780 LCD controller
Back of the PCB
On the top of the PCB, there is the power regulation for the Speak & Spell. Immediately we can see that all the components are through-hole as well as the very large 1W resistor that dwarfs all the other components.
The power control and various analog parts
More components can be found near the HD44780 chip such as diodes, resistors, and capacitors. The potentiometer most likely controls the contrast of the LCD display.
More analog components
Inside the Expansion Cartridge
The expansion is two pieces of plastic that hold each other using clips. Getting the unit open is very easy, so let us see what lies inside the expansion module!
The expansion module
All we find inside is a single DIP IC and an edge connector. The PCB is paper-based (not fiberglass) and shows additional drill holes for other ICs.
The expansion module
The IC in the module is a ROM chip which provides additional programs for the Speak & Spell.
The makeup of the Super Speak & Spell is incredibly simple and clearly orientated for mass production. The whole unit consists of three screws, edge connectors, and ribbon cables that slot in with ease. The display is generic which helps to drive down costs. The DSP, on the other hand, is custom and fitted onto one chip. The ROM uses a very small IC package.
The minimal number of components here clearly helps to keep production costs down which also reduces manufacturing time. A PCB like this could be soldered by an individual in 20 minutes at most. But it would also be difficult to repair because of the lack of IC sockets as DIP ICs are very difficult to remove when soldered in.
This teardown clearly shows the ingenuity of the Speak & Spell as well as the production considerations.
Next Retro Teardown: ZX Spectrum