Planet Sinclair

x The Machines
x Machines: 1970s
x Active Filter Unit
x The Black Watch
x Cambridge / Cambridge Scientific
O DM1 / DM2 / DM235 / DM350 / DM450 / PDM35 / PFM
x Enterprise /
Enterprise Programmable
x Executive /
Executive Memory
x MK14
x TV1A / TV1B / MON1A
x Oxford 100 / 200 / 300
x PP3
x President
x Project 605 / 80 / PZ8 / Q16 / Q30 / Stereo FM / Z-50
x Scientific / Scientific Programmable / Scientific Programmable Mk 2
x Sovereign
x Super IC-12
x Wrist Calculator

Last updated
8 Jan 1998


DM1 / DM2 / PDM35 / DM235 / DM350 / DM450 / PFM

Not the most glamourous products ever produced by Sinclair, it is true; however, the digital multimeter range was the steady-selling bulwark of Radionics' catalogue in the 1970s and enabled Sinclair to produce his more exotic gadgets.

Six digital multimeters, plus one "personal frequency meter", were produced between 1974-79. They were:


Prior to the DM1, digital multimeters were a rather expensive, novel and bulky piece of laboratory equipment, costing rather more than the average hobbyist could afford. The DM1 broke new ground. It was a small handheld unit, housed in a polypropylene case, weighing 1lb 6oz (with battery) and possessing a claimed accuracy of 0.4%. Perhaps most importantly, it cost only 49 + VAT.

It had two big disadvantages, though. The first was that it had some technical drawbacks, such as the use of the unpopular Nixie tube for the display. The second was that (as so often) Sinclair had launched the DM1 without ensuring that sufficient production capacity was in place - the result was that many unfortunate customers suffered delays of, in some instances, months. The company was driven to placing an apology in the electronics magazines. It was perhaps less than diplomatic to blame the customers for the problems:


You surprised us with the overwhelming demand for our new DM1 digital multimeter - which far exceeded even our optimistic expectations.

An Apology.

The result is that many of you who have placed orders have had to wait an unacceptably long time. For this we apologise.

All present orders will be fulfilled by the end of August and shortly after we hope to supply from stock.

Unfortunately, by then the flaws of the DM1 were widely known and demand slumped, just as Sinclair was gearing up to meet it. In November 1974, the price was reduced to 24.95 + VAT. The reduction failed to lift flagging sales. In hindsight, it is perhaps significant that it wasn't even mentioned in a historical account of Sinclair's instrument business, written in 1978.


The DM2, launched in February 1975, was far more successful than its predecessor (as well as being a technically superior product). It had been designed using a mixture of chips and components which were already in service in other Sinclair product, employing just one new chip (from General Instruments Microcircuits). This allowed Sinclair to take advantage of bulk buying to lower the component cost - the DM2 cost 49.95 + VAT.

The meter itself was well-designed, doing its work to a good standard (1% accuracy) and being easy to assemble and test. It immediately found favour in the scientific, hobby, retailing and educational fields, selling very well and making the company a lot of money. For once, production problems had been considered from the outset and high initial demand could be satisfied. Some 30,000 units were sold, 80& of them overseas.

PDM35, DM235, DM350, DM450, PFM

The PDM35 (right) was a direct successor to the DM2, launched in New York in 1977 and aimed at the service and hobby markets. Its US price was $49.95. The DM235, DM350 and DM450 were all developments along the same lines, with an increased number of features - they existed alongside each other with the DM450 at the top of the range.

The multimeters soon passed out of Sinclair's hands, though. In July 1979, Sinclair was eased out of control of Radionics with a 10,000 "golden handshake" and the instruments business was hived off by the National Enterprise Board to form a new company, Sinclair Electronics (to which Clive himself had no direct connection).