Ian, there is no clue on the instruments as to who made them. Just to conclude this thread I'm posting pictures of the three tachos which were bought for next to nothing. Probably a TVR owner somewhere would bite my hand off to have them !!
They are about 100mm diameter.

 

Nice job working out the schematic, but it makes it clear that the chip is not a 555 or 393. 7 is Vcc, 1 is GND, 5 is an output.

BTW, where did the 555 internal schematic come from? Link?

ak

Here's a .gif animation in case you haven't seen it.

 

Ian, there is no clue on the instruments as to who made them. Just to conclude this thread I'm posting pictures of the three tachos which were bought for next to nothing. Probably a TVR owner somewhere would bite my hand off to have them !!
View attachment 90597 They are about 100mm diameter.

The Stuart Warner company I worked for was Icknield Instruments.

Funny thing - I don't actually remember what if any brand they printed on the dials.

Most of the time I worked in the tachogenerator department, sometimes I got called over to cover for people absent from the clean room, making the instrument head movements, but the dials didn't go on until just before the instruments were cased up.

 

#Gerty, its a SN76810P, not a 555 timer....

Here's a .gif animation in case you haven't seen it.

 

#Gerty, its a SN76810P, not a 555 timer....

AnalogKid seemed interested in the inner workings of the 555, I thought he might be interested in the .gif

 

Here's a .gif animation in case you haven't seen it.

The reason I asked about the drawing is that it is one of the rare few that are correct. The animation is not. In the original 555, only the -Q latch output drives anything. It drives the discharge transistor directly, and drives an inverting output stage. The Q output doesn't drive anything internally or externally. It is a minor difference, but it helps to know how parts really work inside.

ak

 

I see the difference, never noticed it before..

 

This is probably not worth starting a new thread for,, When I bought those TVR tachos I was building a 555 based tach for my 1933 Austin. Naturally I searched the net for a suitable circuit and this one came up on several sites. All identical and one gives the source as a Phillips application note. I've tracked it down to HERE page 11

It immediately struck me that a 50ma meter and a 200k pot, at the output and in series with the meter, were not likely to work together too well as 5000 volts would be needed to achieve FSD with the pot at mid position ! Not to mention that I think it would be pretty difficult to even get a 50Ma meter other than one with a shunt.

I found a nice 270 degree meter with 2ma fsd and reduced the value to a few K (can't remember exactly) and it worked a treat. I also left out the resistor from pin 3, output, to the supply rail as I can't see what it's for.

I'm obviously sure that circuit is wrong and the point is that electronic websites must often lift circuits from other sites without building, checking or testing them . As to why Phillips technical published it like this in the first place is a complete mystery...

Unless of course it's me that missed something....if so...put me right..Roger

edit: Ive now tested the first tach - the one in #1 - and it works fine. the meter fsd is about 6Ma.

 

hmm..wonder if its actually an LM2907-8 or LM2917-8?