EEVblog #641 - Dumpster Cash Register Teardown

[Niels]

>Why do they (RDC) denote the 80C186 clone as an RISC/DSP processor?

I will tell you why.  RISC was a major buzzword in the 80s and they were simply trying to jump on the bandwagon.

1980's ? The 80186 was common in industrial automation into the mid 90's.
http://www.cpushack.com/2013/01/12/the-intel-80186-gets-turbocharged-vautomation-turbo186/

The 186 is still available:
http://www.innovasic.com/Products/ia186es-ia188es

The company that I work for replaced the 186 with StrongArm, this turned out to be a bad idea.
Intel stopped production 3 years after introduction despite promises of extended support.

This is a major headache when you need 1-2 years for development, a product life of 8 years, and to support with spare parts for 25 years.

[Stonent]

The thermal head is made by Kyocera using thin film technology. The potted driver ics are basically shift registers with low side mosfet switches on every dot. The dot resistance is typically between 600 and 1500 ohms on those 24v heads. looks like a 200dpi head, each dot is 1/8mm big. The head can be clocked at speeds much higher than 1MHz, typically 5 up to 30 in faster models, and yes, it does draw a lot of current when a lot of dots are fired simultaneously. Today there are thermal printers that can operate at voltages as low as 2.7-3V.

the cutter can do partial or full cuts just by reversing the polarity on the dc motor inside.

Also on the outside of the printer is an SII logo with a circle after it.  That would indicate the full part was made by Seiko Instruments.  They make the "Smart Label" series of thermal printers that are sold at office supply stores.

A bit of trivia on cash drawers, the old parallel port ones in the 80s and 90s could be triggered to open by sending an ASCII CTRL-G (ASCII Beep Code) to the printer port.

I used that trick once to open a drawer when the key was misplaced.

The old DOS command to do it was :

ECHO ^G > LPT1:

The raised caret is put there by pressing CTRL-G not by typing the caret and G.

From windows you can type ECHO ^G and it will make your computer make either a beep or windows alert sound out your speakers if they are turned on.

So, knowing that, if you can figure out the interface for the cash drawer, sending ASCII code 7 might trigger it to open.

[misterm]

I've used several tills like this when younger

As mentioned the latch at the back is to open the drawer without power, this doesn't work if drawer is locked though

the key on the side is to select modes, there are normally keys which restrict which modes you can select to allow say x read but not z reads or programming

L is locked - no transactions
H - I presume this is for normal use
X - X read - a sub totalled list of all sales, typically used during day to monitor sales
Z - Z read - as a bove but zeros the totals, typically used at the end of the day
M - not sure, but probably to program prices for some buttons
P - programming mode

Martin

[David_AVD]

As mentioned the latch at the back is to open the drawer without power, this doesn't work if drawer is locked though

Yeah, it's only an override for the solenoid.  The lock on the front is for when the till is unattended for some time and more secure than putting it into lock mode.

A common practice used to be to leave the drawer ajar overnight if there was no money in there.  This was in case of a break-in so (dumb) thieves didn't destroy the till trying to open the drawer with a lever.

I remember years ago my parents ran a clothing store.  One day there was a power outage for half the day so my dad hooked a piece of fishing line to the override lever and draped it over the top of the till.

That way he could pop the drawer open each time he made a sale.  That was better than leaving the drawer ajar as it still made the "bing!" sound (mechanical bell & striker) when opened via the override so less likely to have a casual theft occur.

[Monkeh]

Make a nice microprocessor controlled toilet paper dispenser with the paper cutting module

I'm pretty sure there is no market for very narrow toilet paper.

Hamsters.

[The Adjuster]

I cant picture in my head how a thermal head like that works. I mean I know how it works, it just doesnt compute, you would need a big thermal mass/heatsink to dissipate energy quickly between pixels, otherwise you wont get sharp edges ... but this thing has no problem with sharp edges, so wtf ?

There are actually two sets of heaters on the head.  One large heater to hold the head just below printing temperature, and all of the individual print elements which can quickly raise (and lower) their temperature to darken the paper.

When I got trained (more then a couple of years ago), the trainer referred to the individual print elements as 'nibs'.

[mxmarek]

cool oscilloscope in top-right corner at 20:30

[f4eru]

maybe you want to unsolder the flat flex connectors, to keep together with the keyboard film.

[f4eru]

Notice how the resistors in the printer are all in series, probably there is a muxing scheme going on, and a residual current into the off ones.

A creative use for the paper cutter ? a confetti machine for Sagan ?
Notice the notch at the center of the blade for keeping a small link so the paper does not fall off.

[phenol]

The resistors are not in series; their hot end is commoned to a single track connected directly to 24v. Also, the off current is the leakage current of mosfet switches, a microamp or less. There are no other heaters and stuff to keep the head warm. A thing like that would waste energy for nothing and this is not a good thing in devices like eft pos terminals where power is on a budget.

[david77]

In my last job we had a nice old cash register made in 1986. One morning I came in and heard a very sickly sounding beeper. As I came closer to the cash desk the smell of cooking electronics became stronger until I could eventually see a constant stream of smoke rising from the cash register.
The poor thing was dying and crying for help.
I pulled the plug and after some head scratching decided to open it up. It used a 6502 processor and a 7 pin matrix printer. The noises this thing made when operating were brilliant. Turned out some caps on the PSU PCB had given up after >25 years. Problem was I really needed the register for daily business and so decided to try and fix it - after all this was an electronics shop I was working in.
This actually worked and the thing booted up after this but as it turned out it had forgotten its configuration. The user manual was of no use to me, I couldn't figure out how to program this old beast so had to call the service tech to re-programm it.
He did it from memory, took him about an hour of keying in arcane codes and the cash register worked again. He told me we were the last ones using this ancient model and he hadn't seen another in service for at least five years. I was impressed that he remembered how to set it up - he's probably one of the better service techs.

All cash registers I've seen so far have that release catch for the drawer on the bottom. You have to be able to get at the money even without power and keys.

The key switch is the mode selector, P is Program mode, X is used for things like cashing up at the end of the day, Z is normal register mode. Have forgotten what the others do but they're usually the same on all cash registers. The keys used for these locks are quite nifty, there are usually at least three different keys, each key performs another function. So there's the P key to get into P mode, then there usually are user keys for the people operating the machine and superuser keys for the boss, for things like cancellations and sub-totals.

[misterm]

On every till (probably 5 or 6 models) I've ever used Z mode is for zeroing, it allows the user to print a summary of whats been sold and then reset that (normally everyday)  so you get a record of daily takings

Martin

[david77]

Yeah, you are probably right, I mixed that up. Funny how fast you can forget things you used to do every day for years  .