DATAMATH

DATAMATH CALCULATOR MUSEUM

Datamath Calculator Museum DCM-50A Playground C-500 Family Adapter

Date of introduction:	March 29, 2025	Display technology:	n.a.
New price:		Display size:	n.a.
Size:	3.2" x 4.0" x 0.85" 81 x 102 x 22 mm³
Weight:	2.9 ounces, 81 grams	Serial No:	0001
Batteries:	n.a.	Date of manufacture:	mth 04 year 2025
AC-Adapter:	n.a.	Origin of manufacture:	USA
Precision:		Integrated circuits:	ZIF-24 Socket, 2*CD4066, CD40106, SN75369
Memories:
Program steps:		Courtesy of:	Joerg Woerner

When we were probing early in 2025 for the first time the 24 pins of a General Instrument GI 250 single-chip calculator circuit soldered on the printed circuit board (PCB) of a Litton Royal Digit III calculator with its odd 4-digit display, we realized that the GI 250 Chip is not compatible with our Datamath Calculator Museum DCM-50A Platform. Three observations of the GI 250 - better known as Pico Electronics' PICO1 Chip - stood immediately out:

• The PICO1 uses a supply voltage of -25 Volts
• The Clock Input uses voltage levels of 0 and -25 Volts
• The 19 keyboard pins are activated with short pulses between each display scan cycle

Probing the GI 251 Chip of a Litton Royal V calculator with a more common 8-digit display resulted in another surprise - and obstacle for the DCM-50A Platform:

• The PICO1 outputs its display information in two groups of 4 digits on the same output pins

On our quest to document Pico Electronics' PICO1 Chip and its many descendants like the General Instrument C-500, C-550, C-560, C-570 and CZL-550, we developed here at the Datamath Calculator Museum three additional tools for our DCM-50A (PLAYGROUND):

• DCM-50A (PLAYGROUND) C-500 Family Adapter: Daughter Board for the DCM-50A (PLAYGROUND) Frame Carrier for General Instrument's C-500 Portfolio
• DCM-50A (PLAYGROUND) KBD102 Keyboard: Keyboard with 20 individual keys to support the PICO1-style keyboard reading
• DCM-50A (PLAYGROUND) Digilent I/O Extender: Plug-In Board to add six additional Input Signals for the Digilent Discovery

To access all features of the early PICO1 Chips, the schematics and layout of the DCM-50A Playground C-500 Family Adapter are providing accordingly:

• DC/DC Converter for high-voltage PICO1 Chips
• Selector Jumper for high-voltage (25 V) or low-voltage (15 V) Chips
• 3 LEDs to signal V_SS, V_DD(LV) and V_DD(HV) voltages
• Header Pins for all DCM-50A Platform Signals provided by the DCM-50A PG Frame
• 100 kHz Clock Oscillator, Selector Jumper for internal/external Oscillator and Level-Shifter
• Driver Transistor for Keyboard Enable Signal and Connector to KBD102 Keyboard
• Digit Demultiplexer for D15, D26, D37 and D48 Outputs with optional Inverters for Select Signals
• Header Pins for various PICO1 Signals
• Patch Field for all 24 pins of the PICO1 Chip

Please notice that the DCM-50A PG C-500 Family Adapter needs to be mounted on top of the DCM-50A PG Frame Carrier.

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