Modification to make an UP timer go down?

Older counters where the counting circuit and the display circuit were separate IC's could be made to count down by modifying the display decoder circuitry. I once did this for a pilot who wanted a similar counter.

The details escape me but essentially it involved inverting the digital BCD signals.

It might be better to seek a timer designed for the purpose.

Neil

I don't know what that means! but in a search of the user manual (which doesn't provide any schematics by the way), the only reference to "BCD" is in the options where it states:

When this option is specified, the unit becomes a CMOS compatible parallel BCD reader. The
generator must have a parallel BCD output.

I don't guess that helps much, but just thought I'd mention it.

You're probably right that I should just look around until I find one actually made to count down, but thought I'd ask since I already have this unit.

Maybe find a schematic to a console with the built in count down timers and build one from that?

RFB

Rich,

Sorry if my post left you feeling that it was snowing...a lot happening but nothing to see.

My intent was to give some idea of what might be involved to modify the counter.

For those wondering what I was saying here's a short lesson. To keep it simple let's count from zero to one on an event.

Counting:
0
1

Now if we invert the 0 and make it a 1 and invert the 1 and make it a zero (negation in the binary digital world) then the count is

1
0

So in effect we are counting down simply by inverting the binary bits.

BCD is Binary Coded Decimal where four bits are used together to represent the digits from 0 to 9. By inverting these four bits the digits could run from 9 to 0. This is just a quick look at the subject but it is not quite this simple and would require what is called "excess three" binary coding.

Another but is some counting ICs have a built in up/down count function which can be controlled by one of the pins of the IC. It would seem that if this is the case with your unit the down count option would have been added as a feature. So, I don't envision an easy fix for you.

Neil

"Another but is some counting ICs have a built in up/down count function which can be controlled by one of the pins of the IC."

Excellent point Neil! Rich, may want to look inside that counter and take note of the IC part numbers and look up their datasheets, perhaps it already can do down counts by either lifting or grounding a simple IC pin!!

RFB

If it's the model with the micro (8749-CT4) the input just past the RESET switch input is the DOWN command input. Just connect a pushbutton switch to ground from this hole (pin 30 on the 8749)

You mean inside the unit, or via one of the holes on the back?.. The main buttons are just start, stop, and reset. On the back are several adjustment "holes", but no reset.. (Back: Front: )

As I mentioned, the guy I bought it from had this thing for over 20 years, and used it to time weather segments recorded for radio stations.
I looked over the manual I downloaded for the ES-520U (mine just says it's a ES-520, but I think it omits the "U" because it's old, yet no different than the 520U.. the "U" just stands for Up timer), I see no reference in the manual about any DOWN circuitry ( http://end80radio.com/equipment/pdfs/U%20Series%20Up%20Timers_Web.pdf )

Nevertheless, I'll take a look inside sometime in the next few days and see if I can find the IC part numbers and/or a micro 8749-CT4 as suggested.

If it can't be modified to count down I'll make do with it until finding a bargain on a nice one that will. (I only have a total of $26 invested in this one)

Just to mention.. the reason I want one is to make it easy during pre-recordings to accurately maintain the lengths of the segments to incorporate into the scheduling, since commercial breaks will be scheduled in specific time intervals.

I've got a couple software freebees that do it, but really prefer a dedicated piece of hardware.

Not completely necessary to have one, but I like little bells and whistles!

Rich Powers has made a point that is significant.

Almost everything can be done on a computer, the Swiss army knife of devices.

But things can also be done by dedicated equipment, apart from a computer.

Very often the dedicated approach is preferable.

We are lucky that computers don't seek revenge when we exclude them from providing certain services.

Speaking of bells and whistles, I just bought a cough-drop! http://www.ebay.com/itm/271103872022

Now all I needs a cold.

What I mean is that the expression "hack" is a euphemism for a cough, as in "a hacking cold".

Anyway, the "Cough Drop" is a neat device, a way to avoid being on the air when you would wish to abruptly re-grab privacy for purposes of suppressing body noise.

What we need next is a "Thought Drop" which would cut our connection when we think of something absurd that's just about to get said.

One eBay purchase at a time.

The 'U' originally meant "Universal" as it pertained to a new slave series which read multiple time codes. It has since come to refer to a whole series of units (including timers) which use the 87C51 or later processors. The older non-U version used the 8749.

I'm referring to the pcb holes to which the switches are wired. The 8749-CT4 (or 87C51-CT5 on the "U" series) is a combo clock/timer firmware which has a down mode. It just isn't used on the 520. The same firmware is used on the 362 up/down models. Its a little more complicated on the U model since the mode select has to be jumpered differently to access the up/down mode, but it can be done.

After watching and waiting, I lucked out and bought a ESE ES-301 which already has the up/down counting capability for a grand total of $28, to replace my ES-520 'up only' unit which I actuall paid more for I think.
It's basically the same unit with more buttons:
It works great, and a lot easier than me trying to modify the other one!