Tuning CMI coin comparitor

[BCD11]

Has anyone tried to "tune" a CMI CC-16E coin comparitor using an oscilloscope? If you have I'd like to hear your opinion of using the oscilloscope.

Thanks,
Bart

[Argentium]

Forgive my ignorance , but what exactly is it ? Something like a Ryedale ? Argentium.

[BCD11]

Hi Argentium,

If you're asking what the CMI CC-16E is, that is the gizmo the coins go through to determine if they are high copper in the case of cents. The CC-16E comparitor also can determine if a quarter of half dollar has a higher content silver than those minted today.

If you're asking what an oscilloscope is, it is a testing device. Beyond that I don't know much about it other than you can use it to fine tune a CMI coin comparitor. I'll defer to others on this this forum that know more about electronics than I do...which ain't saying much.

Me thinks it's time to head to Wikipedia and find out EXACTLY what an O scope is .

[madwest]

Hi Argentium,

If you're asking what the CMI CC-16E is, that is the gizmo the coins go through to determine if they are high copper in the case of cents. The CC-16E comparitor also can determine if a quarter of half dollar has a higher content silver than those minted today.

If you're asking what an oscilloscope is, it is a testing device. Beyond that I don't know much about it other than you can use it to fine tune a CMI coin comparitor. I'll defer to others on this this forum that know more about electronics than I do...which ain't saying much.

Me thinks it's time to head to Wikipedia and find out EXACTLY what an O scope is .

The oscilloscope plots voltage vs time. It would be useful in this context to show that you have selected the optimal sensitivity. My experience is that you can find the optimal sensitivity by trial and success and it is not necessary to tap into the inner circuitry of the CMI.

I am an embedded systems/digital electronics design engineer and have traced the basic circuit of the CMI comparator. It uses fairly basic principles for doing the electronic signature comparison of the subject coin to the reference coin. There isn't much tuning in that regard that can be done - other than the sensitivity adjustment.

There are procedures published by Coin Mechanisms Inc. (CMI) for tuning the comparator. The tuning I have looked into is more in the timing and duration of the accept coil firing. The time delay and time duration of the coil has to match the time between when the coin passes the sensing element and when it reaches and passes the rake. If the coil fires early (or not long enough), the accepted coin gets pinned by the closing rake and causes a jam. If the coil fires late, the accepted coin is pushed to the reject side. If the coil fires for too long, the next coin entering the comparator gets pinned by the rake. The size of the coin is the biggest factor in those timings.

I have not found it necessary to tune the used comparitors that I've gotten. My strong bet is that no one ever really tuned them in the field in the slot machines either. From what I understand, there are flavors of the comparitors that use stored signatures rather than reference coins to determine a match. These types of comparators would likely have more "tuning" required.

[BCD11]

There are procedures published by Coin Mechanisms Inc. (CMI) for tuning the comparator. The tuning I have looked into is more in the timing and duration of the accept coil firing. The time delay and time duration of the coil has to match the time between when the coin passes the sensing element and when it reaches and passes the rake. If the coil fires early (or not long enough), the accepted coin gets pinned by the closing rake and causes a jam. If the coil fires late, the accepted coin is pushed to the reject side. If the coil fires for too long, the next coin entering the comparator gets pinned by the rake. The size of the coin is the biggest factor in those timings.

Thanks for jumping in Madwest! When I said I would defer to others I had you in mind.

When you mentioned trial and success in your post were you referring to adjusting the sensitivity on the comparitor or are you able to vary the timing and duration of the accept coil firing?

Your symptoms indicating improper timing and duration of coil firing REALLY caught my attention as I do get occasional jams caused by a coin getting pinned. After thinking about your comments I'm going to try slowing the feed rate of coins to the comparitor. I'm powering the hopper motor with 24 volts. At that level my Rube Goldberg sorts 325+/- coins per minute with two jams per $25 box of pennies. The jams are a nuisance but what is REALLY exciting is how fast the coins pile up/ back up on the short rail that spans the hopper to the comparitor. I'd better be ready to hit the "Off" switch or I have coins going all over the place!

I read on Rudysdeals website that sometimes and easy fix for a faulty coil is replacing a capacitor in the CMI comparitor. Madwest, or anyone else, do you have an opinion on that?

Again, thanks for all of your help Madwest!

Bart

P.S. Madwest, how are your cascading comparitors working?

[madwest]

. . . or are you able to vary the timing and duration of the accept coil firing?

No, I haven't felt compelled to monkey with anything other than the sensitivity. When I get a second rig set up I might dig into tweaking a comparator or two to work better with dimes. I've had extremely good luck with cents (I suspect it is because they are heavier) and I don't want to rock the boat.

I'm going to try slowing the feed rate of coins to the comparitor.

Slowing it down might help ease the occasional jam. I experimented with that when I was seeing jams but it really didn't help much. The most effective solution for me was to make sure the coin sliding in didn't "slap" around at all when entering the comparator. Once I got it to slide directly in, jams essentially disappeared.

I read on Rudysdeals website that sometimes and easy fix for a faulty coil is replacing a capacitor in the CMI comparitor. Madwest, or anyone else, do you have an opinion on that?

I suspect it is capacitor C1 (10uF, 35V) on the CMI board. That part is the bulk capacitance that supplies the momentary current to activate the coil. One of these days, I'm going to trace the entire circuit. There are 60 components so probably about 30 circuit nodes to figure out on a 2-sided printed circuit board. It would probably take 3-4 hours of study to trace the whole thing and another couple of hours to draw it out in a way that makes sense. I've traced the basic circuit around the dual op amp so I have a start anyway.

P.S. Madwest, how are your cascading comparitors working?

I've got it working in a house of cards fashion. If I get a lull in bags of cents, I'm going to shore the whole thing up and make it more robust - actually, I think I am going to build a second one offline. When/if I get it show worthy, I'll post pics/video.