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Texas Instruments Little Professor (1976 Version C)

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:  n.a.
Batteries:  9V   Date of manufacture:  wk 18 year 1978
AC-Adapter:   Origin of manufacture:  USA (MTA)
Precision:   Integrated circuits:  TMS0975/ZA0356 CSP
Memories:   Displays:  DIS713
Program steps:   Courtesy of:  Joerg Woerner
    Download manual:   (US: 7.3M Bytes)

LittleProf_MTA5077_Back.jpg (140033 Byte)Just a cost optimized version of the original Little Professor. Texas Instruments dropped even the label on the backside of the toy to reduce the bill of material a few cents.

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 C) with Date code 1878 MTA and manufactured in May 1978 in Midland, 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.

The additional PCB found with the Little Professor (Version B) and directly soldered to the power supply pins VSS and VDD of the TMS0975 and its CK clock input pin is gone and the layout of the Main-PCB completely changed to accommodate a TMS0975 chip in a much smaller package. The clock frequency of the TMS0975NL/ZA 0356 BP was lowered with the extra PCB to an unusual low rate of just 150 kHz and we wondered at what speed the revised TMS0975NL/ZA0356 CSP of the featured Little Professor (Version C) would operate. In a first step we calculated the internal clock oscillator frequency of the TMS0975NL/ZA 0356 BP 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. In a second step we applied an external CK signal of 150 kHz to the TMS0975NL/ZA0356 CSP, observed its scan frequency of the display before finally running it from its internal clock oscillator:

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
1878 MTA
CSP 7818
58 Scans/sec 150 kHz 162 Scans/sec 420 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 which seems to operate even at 420 kHz!

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, a Little Professor (Version B) manufactured in December 1976, a TI-1250 calculator manufactured in August 1977, this 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, April 8, 2008. No reprints without written permission.