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Texas Instruments Little Professor (1976 Version B)

Date of introduction:  June 13, 1976 Display technology:  LED-stick
New price:  $19.95, 11.95 Display size:  8
Size:  5.0" x 3.5" x 1.1"
 127 x 89 x 29 mm3
   
Weight:  4.2 ounces, 119 grams Serial No:  0312162
Batteries:  9V   Date of manufacture:  wk 50 year 1976
AC-Adapter:   Origin of manufacture:  USA (LTA)
Precision:   Integrated circuits:  TMS0975/ZA0356 BP
Memories:   Displays:  DIS713
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 7.3M Bytes)

You certainly know this cute math trainer, the Little Professor. Millions and millions were sold in the past 4 decades from this simple but funny educational product. The basic idea behind the Little Professor is opposite to a normal calculator: The child has to type the answer of simple questions like "3 + 5 = ?". You can choose between the four basic math functions and four different grade levels. If the child gives a wrong answer "EEE" occurs, otherwise another of more than 16000 different questions is asked.

This educational toy was rated by Texas Instruments for children aged between 5 and 9 years.

LittleProf_LTA4276_PCB.jpg (131577 Byte)From the technology this First Generation Little Professor introduced in Summer 1976 is related to the TI-1200 calculator of the same year. You'll notice a similar evolution during the production of the Little Professor to optimize manufacturing costs but a minor mishap added one interims step not observed with the TI-1200 and its sibling TI-1250 and all their variations like the fancy T-1225. The pictures on the right compares two Little Professors, an early one and a later one. Here at the Datamath Calculator Museum we named them based on the Revision of the used single-chip calculator circuits accordingly Version A, Version B, Version C, and Version XC.

Dismantling the featured Little Professor (Version B) with Date code LTA 5076 and manufactured in December 1976 in Lubbock, Texas reveals an internal construction very similar to the TI-1200/TI-1250. The single-sided printed circuit board (PCB) is centered around a TMS0975/ZA0356 single-chip calculator circuit and powered by a 9V alkaline battery. The keyboard with 5 rows of keys is borrowed from the TI-1200 although the Little Professor is using only 4 rows of keys.

Looking closer at the picture with the opened housing, you'll notice an unusual gray paper inserted between the keyboard and the PCB and completely removing the keyboard reveals a second, smaller PCB mounted on top of the TMS0975 chip.

The additional PCB is directly soldered to the power supply pins VSS and VDD of the TMS0975 and its CK clock input pin. Measuring the frequency of the CK pin results in an unusual low frequency of 150 kHz and testing a second Little Professor (1976 Version B) manufactured - or should we say repaired - in week 47 of December 1976 gives an only slightly higher CK frequency reading of 158 kHz. To better understand the reasoning why the TMS0975NL/ZA 0356 BP chips are using an external clock oscillator, we calculated its internal clock oscillator frequency by removing the additional PCB. Without direct access to the internal clock oscillator, we simply observed the scan frequency of the display which is directly proportional to the internal or external clock frequency:

DUT Display Scan Rate
with CLK PCB
Measured
CK (Ext)
Display Scan rate
w/o CLK PCB
Calculated
CK (Int)
5076 LTA
BP 7640
60 Scans/sec 150 kHz 130 Scans/sec 325 kHz
4776 LTA
BP 7640
61 Scans/sec 158 kHz 137 Scans/sec 355 kHz

With the internal clock frequency of the TMS0970 single-chip calculator circuits specified at a maximum of 300 kHz, it is obvious that the clock oscillator of the Chip Revision BP has a design flaw and runs much faster than it was designed for. Consequently this design was soon replaced with Chip Revision CP.

The TMS0975/ZA0356 chip is a member of the TMS0970 Product Family introduced in March 1976 with the TI-1200 and based on the TMS1000. The TMS0970 integrated both segment and digit drivers to the TMS1000 feature set allowing for highly cost-optimized designs and paving the way of four-banger calculators with 4-key memory selling below the magic $10 threshold. While the original TMS0970 chips were housed in a standard 0.6 wide 28-pin DIP (Plastic Dual In-line Package with a 0.1 / 2.54 mm lead pitch), started Texas Instruments in 1977 to use a smaller 0.4 wide 28-pin SPDIP (Shrink Plastic Dual In-line Package with a 0.07 / 1.778 mm lead pitch) design.

Preparing our DCM-50A Platform to allow the Characterization of Single-Chip Calculator Circuits of the TMS0970/TMC0900 Family, we studied a TI-1270 calculator manufactured in July 1976, a Little Professor (Version A) manufactured in September 1976, a TI-1200 manufactured in October 1976, this Little Professor (Version B) manufactured in December 1976, a TI-1250 calculator manufactured in August 1977, a Little Professor (Version C) manufactured in May 1978, a WIZ-A-TRON educational toy assembled in June 1978 and a Little Professor (Version XC) manufactured in September 1978.

Learn more about the different Versions of the Little Professor (1976) and its Product Labels on the backside of the calculators.

While the "look and feel" of the four versions of the Little Professor (1976) is identical, did we encountered significant differences in the software implementation of the TMS0975NL chips despite their identical "ZA0356" marking. Follow this link to deep dive into the TMS0975NL/ZA0356.

This first version of the Little Professor could easily recognized by the two sliding switches to the left and right of its face, in December 1978 they were replaced by three additional keys [OFF], [SET] and [LEVEL] slightly disturbing the design of the product. Meet the Little Professor (1978.

Another education toy of this time are the rare MATH MAGIC and its sibling WIZ-A-TRON.

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If you have additions to the above article please email: joerg@datamath.org.

Joerg Woerner, November 11, 2023. No reprints without written permission.