Hornby Zero 1 is a forerunner to the modern digital model railway control system, developed by Hornby in the late 1970s. It was based around the TMS1000 4-bit microprocessor. The Zero 1 system offered simultaneous control of up to 16 locomotives and 99 accessories.The Hammant & Morgan digital train control system is totally compatible with the Zero One,the master controller,"HM5000 Advanced Power Transmitter" boasted TWO sliders,of 14 steps each,direction LED's power LED bar graph,timer clocks,digital display of locos under control,readout of accessories controlled,& ability to attach TWO "Hi-Tec Speed Transmitter" slave controllers HM5500, Zero 1 was released in late 1979.
A multiple train control system named Zero 1 was introduced in late 1979. This control system was a forerunner to the Digital Command Control (DCC) system, an NMRA open standard, which appeared in the 1990s. Though an important milestone, Zero 1 was not widely successful; both the controller units and the decoder modules required for the locomotives and accessories were expensive, but with a clean track and well serviced locos the system worked more or less as advertised.
The Zero 1 system supplied the track with a 20V square wave at the local mains frequency (50Hz in the UK, 60Hz in the US) with a 32-bit control word replacing every third cycle. The decoder module in the locomotive would switch either the positive or the negative half-cycle of the square wave to the motor according to the desired direction of travel. During the transmission of the control word, it would remain switched off. Speed control was achieved by varying the width of the portion of the half-cycle which was switched, in 14 steps.
This system allowed for straightforward implementation with the semiconductor technology of the time, but had the disadvantage that the power supplied to the motor was highly discontinuous - as can be seen from the description above, it took the form of square pulses of a maximum width of 10ms, recurring at intervals which alternated between 20ms and 40ms (for a 50Hz mains supply). This caused the running of the motor to be extremely noisy and rough. Fine control of a locomotive at low speed was also difficult, partly due to the rough running, partly due to the inherent coarseness of a 14-step speed scale, and partly because there was a significant delay between operator input to the controller and response from the locomotive.
Locomotives fitted with a Zero 1 decoder according to Hornby's instructions could not be used on conventional systems, making it difficult to run one's locomotives on friends' layouts or club layouts. It was possible to include a miniature DPDT switch in the installation to enable the Zero 1 decoder to be switched out for use on a conventional system, but the official Hornby information made no mention of this, causing potential customers to perceive a significant disadvantage to the system which did not in fact exist.
Control of points and other accessories was available in a very simple manner. For solenoid-operated accessories (e.g. points, mechanical signals) or accessories involving lights (e.g. colour light signals), track-powered accessory decoder modules, each providing four outputs, were available. Each output could be configured either for burst operation or continuous output, for use with solenoids or lights respectively. Accessories were switched by entering a numeric code on the controller. Up to 99 accessories could be controlled.
Accessories based around motors rather than solenoids or lights, such as turntables, could be fitted with a locomotive module and controlled in the same manner as a locomotive.
Zero 1 had 3 'phased' introductions: Phase 1 = Master controller and basic system (Master controller, slave controller, hand held slave unit and loco modules) Phase 2 = Accessory control (Points, Signals etc.) Phase 3 = Micro Mimic display (Allowed for LEDs to represent status of points and signals on a mimic display panel)
The main master controller unit was discontinued in 1986, and the last time loco modules were listed was in the 1991 catalogue - 'Limited supplies of R955 loco module are available'. Repairs to Zero 1 units were no longer undertaken by Hornby, the reason given being 'Lack of available parts required'.
The system is very reliable, the basic 1980s keyboard design being the main problem on older badly stored master units. It is easily repaired though and can be made to work like new in a few simple steps.Members of the well established & respected MERG group here:-http://www.merg.org.uk/ can buy a complete kit of parts to replace the master controller keypad (on a Hornby Zero 1 controller,or the superior Hammant & Morgan HM5000 Power Transmitter) at a very low price,kit number 71 is the one you need,however,this author has had great success with a simple 3mm square of self adhesive aluminum foil stuff onto the carbon "pills" of the rubber membrane keypad. Loco modules were available in two types. The pre-1981 types were based on a single triac. The square-wave supply and the presence of spikes from the motor and from poor contacts rendered the dV/dt rating of the triac marginal and these units would sometimes self-trigger on the wrong polarity half-cycle, resulting in damage both to the unit itself and to the locomotive motor. The later type, made by H&M, used two SCRs, one for "forward" and one for "reverse", to avoid this problem. Again, the loco modules are easy to repair with the right skills.
The system is still used today by many modellers, as is shown by the demand on sites like eBay for the items in the second hand market. The unused sockets on the rear of the Phase 3 Mimic controller hinted at the way development could have been heading - a light pen socket possibly indicating a link to a computer and control via light pen. Given that this was the era of the Sinclair Spectrum (which was launched two years after Zero 1), the system was perhaps ahead of its time. The DCC system which is today's current standard for digital control of a model railway is similar in many ways to how Zero 1 worked.MERG http://www.merg.org.uk/ has a list of Hornby Zero 1 bulletins & original Hornby documents describing the system further,a "Hornby Zero 1 Protocol Group" exists here :- http://groups.yahoo.com/group/mergZero1 where many pictures,documents & discussions can be found. On eBay & swap meets a vibrant & active market still exists,another British product line ZTC Controls,here http://ztccontrols.co.uk/ has a controller that not only has the Zero 1 protocol,but also has,pure DC,PWM DC,NMRA DCC & 50Hz & 60Hz capability,a truly versatile controller,in fact invented & brought to market by the original inventor of Hornby Zero 1,Mr.Robin Palmer, all praise to him. Zero 1 will do all you ask of it,you must play your part,track cleanliness,ONE DROP of silver loaded paint to code the decoders,both sides of motor brushes insulated with anglers silicone tube,red,black & green wires,soldered,NOT simply twisted & crimped,heat shrink wrap on exposed connections.
Read more about this topic: Digital Model Railway Control Systems, Systems