TAKING CONTROL

Build the house of the future, run a robotic servant, or speak to your Spectrum, all for under £150.

Those boring black interface boxes, which you swore you'd never let into the house, are powerhouses with the potential to control everything in your home that runs on electricity. Watch it switch the lights on and off, the microwave, TV or turn on an intruder alarm.

John Gilbert gives his Spectrum and QL the run of the office. We've never been the same since.

Supplier: DCP or Commotion
Prices: Interpack 1 £43.43; Interpack 2 £34.74; Interpack 3 £43.43' Spectrum Intercard £13.00; ADC Pack £21.70; DAC Pack £21.70; DCP Bus Intercard £13.00; Invertabus £4.30; Powerbus Pack £17.35

Look no further than DCP for a complete control environment which can handle several external hardware devices - robots, turtles, Lego models or stepper motors - all at the same time.

The system comprises three interfaces, called Interpacks, a Spectrum interface and seven related accessories.

Interpack One is the Scientific interface. It contains both digital and analogue inputs. There is also an eight-bit TTL input port and an eight-bit TTL output. You can also get a DCP expansion which allows you to connect other Interpacks.

It's called the Scientific interface because the I/O ports are well suited to situations in which measurement is important, such as gauging temperature or pressure.

The Control interface, Interpack Two, includes an eight-switch contact for digital inputs and six SPDT relays as well as the usual 15-way expansion bus for the potential growth of your interfaces. It's best used for controlling turtle-type robots, buggies and any motor controlled device which does not require precision movement.

If you want precision movement in devices such as robot arms and electronic mice, which have to find their way out of mazes, you'll need Interpack Three: The Stepper Motor. A stepper motor rotates one small step at a time so that you have more control over motion. For instance, a turtle controlled by stepper motors will negotiate difficult corners, stop in a precise position and move in an accurately reproducible way. Similarly, robot arms can pick up delicate objects because of the steady rotation of a stepper motor.

Interpack Three drives up to three 12V two-phase motors using industry standard chips. It also boasts eight buffered switch contact inputs for limit switches and sensors. Again, the DCP expansion bus allows you to put other devices or interfaces on to the back of Interpack Three.

The seven DCP accessories include some nifty hardware and software solutions to control and programming problems:

ADC Pack. Fast analogue to digital convertor. Could be used to turn the motion of, say, a robot into an equivalent electronic signal.

DAC Pack. The converse of ADC. Provides a fast digital to analogue conversion - output from computer to external device. It's controlled by a SV DC power supply and contains a DCP expansion bus.

DCP Bus intercard. Connects one Interpack to another.

Invertabus. Connects two ADC or DAC packs together.

Powerbus. Boosts the power supply when several Interpacks are chained together at the back of your Spectrum.

The DCP range of control interfaces is one of the most powerful and comprehensive around.

INSPECTING THE Interspec

Peter Moore takes a look at a unit to put you in control.

For ZX81 and Spectrum computers, the Interspec from DCP Microdevelopments Ltd. is an add-on interface with a remarkably wide range of facilities. The Interspec provides an 8 input 8 bit A/D (Analogue to Digital) converter, four relay outputs which enable your computer to switch things on and off, four inputs for external switches, an 8 bit input port, 8 bit output port and a facility for further expansion through a 15 way connector called the DCP Bus.

The Interspec is housed in the familiar black plastic case used by so many manufacturers. DCP have worked wonders with this case! It really looks good. The unit lies flat on the desk with the edge connector that plugs into your computer at one end of the case. No rear edge connector is provided on the Interspec so ZX81 owners who have Sinclair RAM packs are left to fend for themselves.

The remaining three sides of the case have rows of sockets for external connections. 2mm sockets are provided for the 8 analogue inputs, four switch inputs and four relay outputs. These provide good plug retention and no problems should be experienced with wires coming unplugged. 0.1" 'Molex' connectors are provided for the 8 bit input and output ports and the DCP Bus.

The Interspec electronics are mounted on a double-sided printed circuit board and the component layout is neat and professional.

The instruction booklet gives full details on programming the Spectrum and a supplementary leaflet contains two short machine code subroutines which provide the equivalent of IN and OUT commands on the ZX81.

A TO D INTERFACE

An A/D (Analogue to Digital) interface converts a voltage at an input to a number in the computer. Eight analogue inputs are provided on the Interspec which can be used for signals in the range 0 to 2.7 volts. DCP quote a tolerance of +/- 20% although on the unit I tested, accuracy was well within 10% in the range 0 to 2 volts. The interface has a resolution of 10 millivolts (10mV); if you were to put a signal of 10mV in, your computer would read this as 1:500mV would read as 50, while 1 volt would be 100.

Programming the A/D interface is easy. Each of the 8 analogue inputs has a number from 0 to 7. To select one of these inputs, the command OUT 31,n is used where n is a number from 0 to 7: then LET x = IN 31 reads the numerical equivalent of the voltage on the selected input to variable x. The OUT command must be repeated before each IN since this initialises A/D conversion. The Interspec uses the AD0809 A/D chip; DCP quote the conversion time as being typically better than 1 millisecond.

While anyone familiar with electronics theory knows how a graph showing the charge and discharge curves of a capacitor will appear, seeing it happen in real time with the computer drawing a graph on the screen is a fascinating demonstration of the theory.

I must admit to spending some time charging and discharging capacitors and watching the varying voltages across them being plotted by my Spectrum. A simple D/A (Digital to Analogue) circuit using the ZN428 is described in the Interspec literature, details of the connections to be made to the Interspec DCP Bus are included. Personally I would have liked to see this built into the Interspec - perhaps in place of one of the A/D inputs; however the extra circuitry is very straightforward and should not require much experience to build.

RELAY OUTPUTS

Four subminiature relays are built into the Interspec. These have contacts rated 1 amp at 12 volts. Each relay output has a binary value of 1, 2, 4 or 8. Alongside these outputs is a socket marked 'relay common' to which are connected one half of each of the four pairs of relay contacts. These four outputs can be used to directly switch small motors, solenoids, lamps etc. If you want to switch mains powered equipment on and off, you will have to use the Interspec relays to switch larger 'heavier' relays whose contacts are used to switch the mains. Again, programming is by means of IN and OUT commands. OUT 63,4 would switch relay four's contacts on; OUT 63,0 would switch all four relays off.

Four inputs for switches are provided which give an easy means of connecting external switches to your computer. A fifth socket supplying + 5 volts is mounted next to these. Switches should be wired so that they connect this 5 volt line to a switch input. Programming for the switch input port takes the form LET X = (IN 63) - 240. Each of the four inputs has a binary value of 1, 2, 4 or 8. So if switches 1 and 4 were closed, for instance, the variable x would return the value 5 2, 4 or 8, So if switches 1 and 4 were closed, for instance, the variable x would return the value 5 (i.e. 4+1 = 5).

EIGHT BIT PORTS

The 8 bit input and output ports are programmed with IN and OUT 95. IN 95 reads in a byte from the 8 bit input port, while OUT 95 outputs a byte of data (i.e. a number from 0 to 255) to the 8 bit output port. Data is latched to the output port and remains constant until changed, so this port could be used, for example, to light LEDs.

DCP have also devised a simple 15 way connection system which allows you to expand your computer's capabilities with further electronics. DCP market other equipment which plugs into this DCP Bus including a D/A converter and a fast A/D converter. Both these devices cost £19.95 + £1.95 postage.

CONCLUSION

The DCP Interspec is un doubtedly a very useful tool for educational purposes and should prove an interesting accessory for computer and electronics hobbyists. At £49.95 + £1.95 postage it is perhaps a little expensive for the average micro user but you get a lot for your money.

The Interspec can be obtained directly from DCP Microdevelopments Ltd. at 2, Station Close, Lingwood, Norwich.

THE COMPLETE EXPANSION UNIT

DCP Interspec pack is a combination of several other packs produced by the same firm into one box which fits the ZX-81 or the Spectrum. It contains an 8-bit input and output part, four relay-isolated outputs rated at 24V-1amp, four switch inputs - for joysticks, thermostats - and an analogue-to-digital converter with eight channels. That is an appreciable amount in a box only 4.5in. long by 3in. wide and 2in. tall.

The Interspec has an expansion bus at the back which provides the data, read and write control signals, plus two device-select pins to add to your own interfaces. All are fully-decoded, to the limits allowed on eight address lines, and work very well.

DCP Micro Developments Ltd, 2 Station Close, Lingwood, Norwich NR13 4RX. Tel: 06023-712482.

GETTING EVERYTHING PAST THE SENSOR

On its own a computer is pretty useless. It's only when it is given some form of input - like a keyboard - and an output, for example to a TV, that you can do something with it.

But why stop there? A computer like the Spectrum can, with the right input/output (I/O) ports, do a great deal more: switch on and off electrical appliances, control robots or turtles, react to all sorts of electric sensors.

The whole area of control applications for home micros is still quite young and using your micro to throw relays to work household appliances or simple robots is still something for which you will need a little knowledge of basic electronics.

A good place to start, though, is with the Interpack 1 from DCP. The small 'black-box' device offers a varied range of I/O ports and is available from Commotion, which specialises in control applications, turtles and robots.

The interpack provides three ports.

Port A has an 8-channel ADC - Analogue to Digital Converter. What this does is convert any voltage applied to one of its channels of between 0V and 2.5V into a number which the computer can read. The size of the number corresponds to the voltage: the higher the voltage the higher the number. For example if the voltage came from the output of a volume control the computer could tell me when it was too loud, or if the same control was put into the joint of a robot arm the computer could tell what angle it was set.

Port B is both an input and an output. The output is in the form of four relays it can turn on and off, which in turn could power electric motors in a turtle or low-power lamps. The input is in the form of four contacts which can detect if a switch has been turned on. These could be used in a burglar alarm to sense when a window has been left open, or on a turtle to see if it had run into something.

All connections to these four Part B relays are via small jack plugs, like those used by Lego in its electronic kits.

Lastly, Port C provides eight lines of TTL-level I/O. These are the sort of signals computers and similar equipment easily recognise. These are more for the electronic enthusiast who wants to wire up the latest piece of wizardry.

At the back of the Interpack 1 is another set of connectors for other DCP products which provide yet more I/O.

The Interpack 1 is a useful low-cost introduction to I/O, robotics and computer control. If you want to get more out of your computer, put your thinking cap on and make your Spectrum earn its living.

Interpack 1 is £49.95, and ZX Intercard - the accompanying software module for the Spectrum - is £14.95.

Both are available from Commotion, 241 Green Street, Enfield EN3 7SJ (Tel: 01-804-1378).