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Calculators: Handheld: Sinclair Hybrid: Rivendell Cinetron Calculator/Counter

(C) Emil Dudek 2010

(C) Emil Dudek 2010

(C) Emil Dudek 2010

Making no attempt to hide the fact that this is a calculator hybrid - perhaps they wanted to live of the back of the Sinclair marketing campaigns of the time?
The two piece plastic two-tone main case was much used in the 1970s by hobbyists (myself included) as it was readily available, cheap and of high quality.
Any information about this or the company would be gratefully received.

Size (approx):

108mm (max) x 190mm x 59/82mm (box/max)  (w,h,d)
Weight 432g excluding batteries
Power:  9V DC, 6 x AA size batteries.  It accepts an adaptor (undefined, though 6V centre positive just works) through a socket on the top side to the far left.  The batteries are held in three four-way holders rigged to take six batteries.
Case: Large two-piece soft matt black plastic case.  The purple display filter is titled at about 25 degrees, allowing for the large top area to store the battery.  It works well as it has a bright but limited angle display  Big buttons make a big click but work well to this day.  This is mounted on a dark and light grey plastic box with a blue, red and black printed metallic label over the top area and blue printed logo label below.  A 6-way DIN connector sits on the right hand side in line with the LED bar display.
Display: 8 digit red LED with bubble lens and no ninth digit.  An additional ten-bar red LED display is mounted above the main calculator display.
Features: 4 function calculator with selectable constant: hybrid configuration set to operate as a counter.  
Age: 1975
Manufacturer: Rivendell, no other information.  
Comments: Rare hybrid model that looks like it may have been a frame counter for the movie or video lab/studio. I cannot find out anything about this company or product so suspect it was a small specialist electronics organisation.  The extra circuitry used LF components (BC108s and the DIL reed relays), so this was not designed for higher frequencies: medium audio at most.

Components: Additional to that of the calculator:
1 x IC switch: RS DIL reed relay A 349-383, 14 pin DIL 0.3" black plastic
1 x IC: SW7400-N 7423 (date code week 23 of 1974) (TTL logic gates), 14 pin DIL 0.3" black plastic
1 x IC: NS DM7490N 7537 (date code week 37 of 1975) (TTL decade counter), 14 pin DIL 0.3" black plastic
1 x IC: SW74132-N 7436 (date code week 36 of 1974) (TTL Schmitt trigger), 14 pin DIL 0.3" black plastic
5 x transistors
1 x diode
9 x capacitors
13 x resistors
Boards: Additional to that of the calculator a small single board is mounted in the top section.  A 6-way battery holder sits attached to the rear section of the case.
Construction: Remove the four large screws from the base and the case will easily separate.

Logic comments:

For general logic comments about the calculator see Sinclair Oxford 100 Type 1
The left hand switch appears to toggle between line input and manual input of the counter
The right hand push-to-make switch increments the LED bar display

With the rear of the case removed you can see the exposed calculator and the add-on board.  The brown stain was a (now rotted) foam separator.  The board has been designed and etched so this item is not a "back-street" one-off product.