Paper tape punch interfacing?

[Tony Duell]

> 
> I have a Tally 420PR paper tape punch mechanism with no
> electronics, and would like to build a driver board for it. I have

I knew I had the Tally Model 420 manual somewhere, and amazingly it was 
where I thought I'd put it....


> a DEC PC8E (M840) interface card for my 8/A project which would be
> the logical starting point. I was able to find a schematic of the
> punch online but no other manual or information.
> 
> The solenoids run on -48VDC but I have no data as to pulse widths

There are 2 versions : 24V and 48V. The way to tell them apart seems to 
be to measure the resistance of the coils -- 48V ones are 220 Ohm, 24V 
ones are 50 OHm (all should be the same in a given machine). FWIW, 
there's a recomended suppression circuit in the manual consisting of an 
RC series circuit in parallel with each coil. For 48V, use 10 Ohms and 
0.5 uF (I guess 0.47uF is near enough), for 24V use 5 Ohms and 0.7uF (4.7 
Ohms and 0.68uF?)

The manuals says 'The escapment assmbiles for the capstan drive and 
perforator drive mecahnisms require dc pulses of 4.5 +/- 0.5 milliseconds 
duration at 48 or 24 +/- 10% volts according to customer requirements. 
One pulse must be supplied for each movement of the tape and for each 
character to be punched. Puchn pulese for all 8 channels are normally 
derived from a common pulse, but if individual pulse sources are used 
for each channel, all pulses for any individual character must be 
simultaneosus within +/- 0.5 millisecond'.

It also claims it'll go up to 60cps, which gives the maximum repitition 
rate for these pulses. You can go as slowly as you like, it's entirely 
asynchronous (unlike, say, a BRPE, which can be a right pain to interface).

The manual also says 'CAUTION: A steady curret of the rated voltage will 
burn out the coils.'

I assume you know the machine runs in an oil sump, level to be kept 
between the min and max marks, The recomended oil is 'Light turbine oil 
viscosity 160 SSU. Texaco A R & O or equivalent'. You should alos 
lubricate the motor bearings twice yearly (Bardahl BOA30 or equivalent) 
and the folloing points every 500 houes : Bearing bushces in the 
capstan drive, reel drive and ideler (Bardahl BOA30), wipe each armature 
and pole face and put  1 or 2 drops of lubricant on the felt pads 
(Bardahl BPA30, do not overlubricate) and one drop of lubricant on each 
armature tip (silicone fluid 250cs, Dow Corning 200). 

Don't ask me where to get these lubricants....

> and duration, or even the speed of the mechanism (30cps?) There
> are solenoids for each of eight (data) punch pins, a sprocket-hole
> punch, tape feeder (which also operates a contact to actuate the
> forward ratchet mechanism), and reverse ratchet (for rubout I
> assume).
> 
> Any ideas? I am not sure how much of the timing is generated by
> the M840 card and how much by the M710 inside the PC04 assembly.

Having built a PC04 (well, converted a PC05 into one...) I seem to 
remember that the DEC punch mechanism is a synchronous one. The motor 
runs all the time, turnign the camshaft, you get a pulse per revolution 
fro ma pickup head, and the interface then drives solenoids to operate 
the punch pins and feed mechanism based on that timing. Now whether if 
you fed a suitable clock into the inferface card, you'd get out pulses 
that could be used to drive the asynchronous Tally mechanism I don't 
know, but it seems like a starting point.

> 
> Also, the connector is a Continental 25034-16P. Does anyone have a
> mating female connector?

Alas the manaul tells me that a mating connector is supplied with the 
machine. Not a lot of help...

-tony