DATAMATH CALCULATOR MUSEUM |
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) |
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.
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.
If you have additions to the above article please email: joerg@datamath.org.
© Joerg Woerner, April 8, 2008. No reprints without written permission.