There were at least three commercial versions of the VELA, the Mark I, Mark II and VELA PLUS. Each one was a refinement of the previous version with the main hardware remaining the same throughout. Although the VELA versions had specific differences and variations, it is apparent from the VELA's I've come across that there was a mix and match approach to the building of the VELA hardware dictated by the availability of parts at the time each unit was built.
In some marketing materials, it seems that some early pre-production VELA devices were used as the source for the photo's of the device. The only discernable differences from the production models are the physal construction of the fascia panel, being made up of several parts instead of being a single assembly and the increased size of the reset button.
The VELA Mark I was the first commercially available VELA and although it had many of the features of the Mark II and VELA PLUS, it lacked any form of Auxiliary power output and required a daughter board to be plugged in to allow for the expansion of the functionality by adding extra ROMs.
The motherboard in the Mark I was split into two sections. The first connected to the power and keyboard assemblies and is responsible for all the processing that the VELA performs as it contains the sockets for the 3 ROMs, the CPU and three PIA's. The digital output for the VELA is also present on this board.
The second board in the photo below is connected by way of a ribbon cable (pictured) to the first and provides the analogue input buffer circuitry, output to the LED array and output to an oscilloscope,
Obvious differences in the design beyond the split motherboard are that there is no provision for a battery backup facility in the Mk I VELA and the 1A 250V rated fast blow fuse was mounted on the motherboard rather than the externally accessible fuse holder fitted to later models.
Externally, the keys on the membrane keyboard had squared off corners where the later models had rounded corners and the channel selector switches showed not only the voltage range selected but the display multiplier also.
Whilst the VELA Mk I had the same output connections as the later models, the arrangment of the connectors was significantly different due to the dual PCB design.
The Mark II VELA carried through several refinements to the design of the system and included extra features such as extra ROM sockets for future expansion, a 70mA 5VDC power output and revised ISL ROMs to take advantage of the extra expansion capabilities. The most significant change however was the move to a single PCB motherboard and support for battery backup for "in the field" data gathering.
My VELA is a Mark II VELA, however it uses the power connector that was specified for the Mark I version rather than the DIN plug that was specified for the Mark II and PLUS versions of VELA.
As you can see from the image below, the VELA PLUS underwent a revision to the front panel with a clearer segmented layout helping users follow the flow of configuring the VELA for experiments and subsequent data transfer. The VELA also had a name change from "Versatile Laboratory Aid" to "Versatile Laboratory Instrument". Internally the circuit board was revised again and the ISL ROMs were re-built with several changes making them incompatible with previous versions of ROMs available for the VELA.
Changes to the circuitry included swapping the ZN449E Analogue to Digital converter for the more accurate ZN448E and revising the pre-amp analogue inputs to provide reduced signal noise to the A to D converter. The signal noise was reduced by the use of a CD4049 mounted on a daughter board that cleaned the signals being fed into the ZN448E ADC chip. This applied to VELA PLUS devices based on the VELA Mark II circuit board. VELA PLUS devices using version 3 of the VELA circuit board simply had a ZN448E fitted to the motherboard and used significantly revised input circuitry.
The board was also revised to remove the two 1.25V channel inputs on the rear panel of the VELA which can be seen in the photo's below.
VELA PLUS photo courtesy of Robert Boyd (Glossop High School)
VELA PLUS photo courtesy of Robert Boyd (Glossop High School)
With the advent of the VELA PLUS, Educational Electronics had also begun to produce custom versions of the VELA with slightly different ROM images which removed some of the original ISL1 programs and replaced them with some of the utilities from ISL2 and ISL3 which provided a more rounded set of functions in one ROM but reduced the number of applications the VELA could be used for. One such VELA derivative was the RS Components Multi-function intelligent data logger which had the RS Components part number of RS 611-975
As you can see from the photo's the device is visually identical to the VELA PLUS however the ROM image that runs this particular version of the VELA is significantly different where programs 7 to 12 are different to the programs in the original VELA ROM and there are no programs numbered 13 to 15. The manuals too reflected the changes including it's description with the use of the VELA name removed completely.
I'd like to thank Jon Neville-Green of The Discovery Academy School in Stoke-On-Trent who kindly arranged for me to obtain their VELA which had been gathering dust in exchange for a donation to the Science department at the Academy. Thank you very much.
I'd also like to thank Cathy Herriman of Sherborne School for providing me with a full surplus set of manuals and supporting books and documents for the VELA in exchange for a donation to the School funds. Thank you.
Finally, I'd like to thank Mr Robert Boyd of Glossop High School in Adelaide and Dr. Ashley Clarke (one of the original creators of VELA) who have both contributed information in various e-mails that has allowed me to build up and present a wider picture of the VELA data logger and what it could do.
The following ROM images are Mk I EPROMS and are incompatible with the ISL1* ROM from the VELA Mk II. You can use the Mk I ROMs in a VELA Mk II or VELA PLUS but there are several differences in the data formats they produce when exporting from the VELA so when sending data to a microcomputer, it should be told it is connected to a Mk I VELA.
The following ROM images are for the VELA Mk II as indicated by a red *.
The following ROM images are for the VELA PLUS as indicated by a green *.
This final ROM is the RS Components ROM image that replaces ISL1* for their re-branded Multi-function Intelligent Data Logger.
The following datasheets cover all of the IC chips that are used in the VELA Mk. II data logger.