Sheet Lens
An efficient magnifier able to enlarge a whole A4 size page, and weighing only 35gms (1 1/4oz) is not available from Magnifiers & Microscopes (3, Approach Road, Taplow, Maiden head, Berks SL6 ONP. Tel. 01-437 2944).
Essentially a flexible acetate sheet of approximately A4 size, each unit has embossed in it (as a pattern of concentric rings) the profile of a high grade magnifying lens, telescoped together into a surface which is virtually flat but with the optical properties of the lens. Known as a Fresnel lens, this construction has been used for years for lighthouse lenses and similar large optical systems, to reduce their weight.
Recently Fresnel lenses have been used on rear windows of buses to assist the driver.
The M&M sheet magnifier has adapted the Fresnel principle to precision pressing. with concentric rings spaced 0.5 mm apart. Each ridge accurately represents the relevant curvature of a lens which would be prohibitively expensive and heavy as a solid glass (or plastic) lens.
The sheet magnifier is extremely flexible, easily carried in a briefcase and requires no frame or mounting.
Held at a convenient reading distance above an object, the sheet magnifier offers a magnification of about 1.5 to 2x.
It is therefore an effective aid to many visually handicapped people, as it allows a whole book page to be viewed at once.
It is equally useful to normally sighted people for reading maps, checking intricate work and similar tasks--such as checking circuit layouts, PCBs and soldering.
The M&M magnifier retails at about £ (x 1.4 USD) 2.60 +VAT and is normally supplied (and used) in a clear acetate envelope which protects the unit against abrasion and scratches
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Battery Control
Batteries need not fail as a result of overcharging. S & W Battery Charging Systems have developed a plug-in module that can be fitted to any battery charger to adjust the output according to the battery's need. The controller will allow full charge to be delivered into a flat battery, but when the voltage rises the current will reduce to a safe level.
The battery may be left on without fear of overcharge. This type of control is essential when using new re-combination sealed lead acid cells.
The 10 Amp version is encapsulated and tamper-proof. It is available in fixed or adjustable voltage mode for use on various types of cells. Although designed for industrial use, the controller can also say S&W be fitted to any existing uncontrolled charging system.
For further information please contact S & W Battery Charging Systems Ltd., Nailsea Trading Estate, Southfield Road. Nailsea. Bristol BS19 1JL. Tel. (0272) 855161.
Or build the Intelligent NiCad Charger on page 00.
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Anti Static Containers
Components can be protected against damage from electro-static discharge by using this Appollo racking system. This equipment consists of a grounded aluminum frame, and conductive containers in a range of sizes.
Each aluminum frame offers a press stud for connection to earth or an anti static bench mat using a grounding strap. The extrusion provides a number of lips to accept clip-on component trays.
The trays are electro-conductive containers made from a carbon-loaded compound with a volume resistivity of 100 ohm-cm. The trays are colored black and carry the standard black and yellow static-sensitive warning label, as well as an identifying marking on the underside.
For further information contact Dage (GB) Ltd, Eurosem Division, Rabans Lane, Aylesbury, Bucks HP19 3RG. Tel. (0296) 33200.
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New Meters
Alcon Instruments have introduced the Super 20 and Super 50 multimeters from the Miselco range.
These new meters include a fool proof protection device on all ranges, against any sort of mistake, only excluding the top 10A and 3A ranges, say Alcon. The two are similar in almost all aspects, but have basically different movements offering sensitivities of 20kR/V and 50kR/V on both AC and DC respectively.
Each instrument has 39 ranges from 100mV (150mV for the S/50) to 1 kV DC and from 10V to 1 kV AC. Current ranges extend from 50uA to 10A for the Super 20, and from 20uA to 3A for the Super 50 on DC, and from 3mA to 10A or 3A on AC. The resistance ranges are five, covering from 5kR to 5MR f.s.d.
An optional high voltage probe extends the upper limit of the DC ranges to 30kV for TV and the like.
Accuracy figures are 2% f.s.d. for DC and 3% for AC and 1% of center scale for resistance. These values, coupled with the figures noted, make the Super 20 a good general-purpose multimeter, and the Super 50 well suited to the specialist electronic measurements for which it was designed.
Both instruments are protected by a quick-acting .quartz-filled 1A fuse, by back-to-back diodes and by an internal (triac) that allows the instrument to stand overloads on all ranges (3A and 10A excluded) without damage.
Further information from Alcon Instruments Ltd., 19 Mulberry Walk London SW3 6DZ.
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Roving Artist
If you have £ (x 1.4 USD) 250 to spare and want a printer/plotter robot. check out the Penman by Penman Products Ltd., 8 Hazelwood Close, Dominion Way, Worthing, W. Sussex BN14 8NP. Tel: (0903) 209081.
The Penman "combines the functions of the precision three color plotter, printer (down to characters 1 mm high), turtle, mouse and robot with optical sensors and collision detection." Basically, the machine will draw lines and curves on a flat piece of paper, without any staircasing effect. At £ (x 1.4 USD) 250 it is not quite a low-cost plotter, but certainly a middle-range one.
Penman themselves provide utility packages for the Apple II, BBC Micro and IBM PC, and other packages are said to be in the pipeline.
New User Group
Dear Editor, I am writing to inform your publication that a new computer club has been formed in the Whitehaven/Workington area.
The club, which will be known as 'The West Cumbria User Group', will cater for computer and electronics enthusiasts.
Activities to be undertaken will include open evenings, computer courses, and working on various computer and electronic projects (at present these include 6502 & Z80 machine code as well as EPROM programmer, graphics digitiser, lightpen, and a speech project).
For details of the User Group, and dates of meetings, ring P. Majid (0946) 62732 or K. Purkiss (0946) 66586.
Yours faithfully, A. Johnson, SECRETARY.
There you have it as we heard it. Ed.
New Shop Bradley Marshall have opened a new shop (opposite their old shop) on the Edgware Road in London. A free catalog is available listing some of their 5000 stock items.
Bradley Marshall Ltd., 382-386 Edgware Road, London W2 1BN. Tel: 01-723 4242.
Also see: PCB Page