DATAMATH CALCULATOR MUSEUM

Heathkit Aircraft Navigation Computer OCW-1401

Date of introduction:	1978	Display technology:	LED-modules
New price:	$169.95 / $274.95	Display size:	14
Size:	6.3" x 3.1" x 1.7" 161 x 80 x 44 mm³
Weight:	10.6 ounces, 302 grams	Serial No:	37313
Batteries:	4*AA	Date of manufacture:	year 1979
AC-Adapter:		Origin of manufacture:	USA
Precision:		Integrated circuits:	3 * Mostek MK3870
Memories:
Program steps:		Courtesy of:	Joerg Woerner
		Download manual:	(US: 4.6M Bytes)

You are right - there is no connection to Texas Instruments! But - to be honest - it is one of the best engineered calculators.

If we trace back the Aircraft Navigation Computers back to their roots we locate two different approaches:
Simple models introduced around 1980 like the Jeppesen Sanderson avstar or the prostar based on scientific calculators and more complex products like the USMC HARRIER based on programmable calculators.

This OCW-1401 started already in the year 1978 a third approach: Powerful Navigation and nothing else! Later products like the Navtronic Explorer (1983) and the Jeppesen Sanderson Techstar (introduced 1992) continued these kind of products.

You are familiar with this OCW-1401? Then you know the calculators sold by National Semiconductors. On a first view the calculator looks like a scientific calculator from National Semiconductor, e.g. the Model 4650. Indeed, the keyboard and the display of them are identical.

The OC-1401 was sold as kit, the OW-1401 was factory wired. Both included:

• The calculator
• A glare screen for the display.
• A cigarette lighter plug for external power.
• A hard case to protect the equipment.

Dismantling this Heathkit OC-1401 Aircraft Navigation Computer reveals the complexity of the product. Three mask-programmed 8-bit single-chip microcomputers manufactured by Mostek (MK3870-MK14103 to 14105) and three other integrated circuits (Fairchild F3539, National Semiconductors DS8664 and DS8667 display drivers) on a large printed circuit board. To our knowledge the most complex pocket calculator ever produced - like most Heathkit products it was sold as a kit! A factory assembled version was available at $274.95. Find more information about the MK3870 here.

More astonishing is the usage of the calculator. In comparison to other flight computers you don't need a 100+ pages manual. Three modes are available:

• Preflight: You have to key in all preflight data with the orange keys.
Data is saved in standby mode while transport to airport.
• In-flight: You set the time and key in all necessary data with the yellow keys.
• Navigation: With the green keys you get all navigation data.

If we trace back in the history of electronic flight computers we discover: The Commodore N-60, this Heathkit OCW-1401, the navtronic 16 and the Texas Instruments TI-58 (with installed Aviation Modul). Heathkit published a small comparison table:

Features	Heathkit OCW-1401	Commodore N 60	Navtronics 16	Texas Instr. TI-58
Flight Leg Entries	Up to 9	1	1	1
Continuous Data Update	YES	NO	NO	NO
Built-in Clock/Timer	YES	NO	NO	NO
Fuel Warning	YES	NO	NO	NO
Built-in Diagnostic	YES	NO	NO	NO
Scientific Functions	YES	YES	NO	YES
Internal Program Built-in	YES	YES	YES	NO
Price	$169.95 (KIT)	$99.00	$197.50	$149.95

All were introduced in or before 1978, two years before the Jeppesen Sanderson avstar based on a Texas Instruments TI-35 appeared.

Don't miss the Tamaya NC-77 Astro-Navigation Calculator!

MK3870

Fairchild Semiconductor reached in June 1975 an agreement with Mostek to second-source the F8 8-bit microprocessor system and both companies worked in 1976 on combining the two-chip 3850/3851 solution into a single-chip Microcomputer with 2,048 Bytes of Program ROM. It was ironically Mostek who not only won the race with introducing their MK3870 a few weeks ahead of Fairchild's 3859, their MK3870 design was using a single +5V supply while the 3859 still relied on dual +5V/+12V supplies. Fairchild consequently dropped the 3859 and licensed instead the 3870 back from Mostek - becoming now the second source.

Technology

The MK3870 is a complete 8-bit microcomputer on a single MOS (Metal–oxide Semiconductor) integrated circuit. It is manufactured in a n-channel ion injection silicon-gate technology compared to the ion-implantation, depletion-mode load, p-channel MOS metal-gate process of the MK5020. The MK3870 can execute the F8 instruction set of more than 70 commands, allowing expansion into multi-chip configurations with software compatibility. The device features 2,048 bytes of ROM, 64 bytes of scratchpad RAM, a programmable binary timer and interrupt, 32 bits of TTL compatible I/O and a single +5 V power supply requirement.

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