Cheapest way to detect a coin drop through a slot?

[SA Dev]

Hi,

I'm building an arcade machine and the switch that senses the coin dropping
in a slot trips up and sometimes goes off twice, or not at all. The problem
is that a wire the switch uses to trip itself slows the coin and bounces it
around a little before allowing it to drop all the way. Could something
like a photoresistor (is this what they are called?) and a LED do this
without mechanically touching the coin? What is the cheapest/easiest way to
do this? When the coin is sensed I need two wires to be shorted...

Thanks,

SA Dev

 

[Rene Tschaggelar]

Hi,

I'm building an arcade machine and the switch that senses the coin dropping
in a slot trips up and sometimes goes off twice, or not at all. The problem
is that a wire the switch uses to trip itself slows the coin and bounces it
around a little before allowing it to drop all the way. Could something
like a photoresistor (is this what they are called?) and a LED do this
without mechanically touching the coin? What is the cheapest/easiest way to
do this? When the coin is sensed I need two wires to be shorted...

Are you interested in detecting a round piece of metal or make sure
an actual valid coin was inserted ?
For the second, you have to measure a lot more such as diameter,
alloy, image.

Rene

 

[Jim Thompson]

Are you interested in detecting a round piece of metal or make sure
an actual valid coin was inserted ?
For the second, you have to measure a lot more such as diameter,
alloy, image.

Rene

Yep, I did some designs for a company called "Coin Accepters" *many*
years ago.

...Jim Thompson

 

[SA Dev]

Hi Rene,

Are you interested in detecting a round piece of metal or make sure
an actual valid coin was inserted ?

There is a coin mech that already does the sorting to make sure the coin was
valid. If a coin makes it to the place I want to attach some sort of
sensor, it has already been validated. I just need to detect that it passes
through a small chute without physically touching it... That is why I was
thinking of something like a light/LED sensor/detector...

Thanks,

SA Dev

 

[Peter O. Brackett]

Jim:

[snip]

Yep, I did some designs for a company called "Coin Accepters" *many*
years ago.

...Jim Thompson

[snip]

Hmmmm same here...

but I did designs for a company, now defunct, called "Electro-Vend"...

Now I wonder... "Coin Accepters" or "Slug Rejecters", which one is most
difficult?



All depends upon the viewpoint.

In my invention, I used two balanced bridges, each in an active bridge
detector
circuit, each using an inductor surrounding the coin chute, but oriented in
two
perpendicular directions.

One coil had windings parallel to the coin face, the other coil had windings
surrounding the chute and coin.

The first coil induced high circulating eddy currents and the bridge
unbalance
due to the excess eddy current resistance caused by the currents circulating
in the sample coin measured/indicated the electro-resistivity rho
as the coin passed by. The other perpendicular coil induced smaller eddy
currents
and measured mainly inductance and hence magnetic permeability mu as the
coin
passed by.

By simultaneously measuring both electro-resistivity rho and magnetic
permeability mu
on one known coin sample one could accurately determine the coin's size,
value, and
presence...

We built several prototypes and they worked very well... Electro-Vend
applied for
patents on my invention, but went under when their seed capital ran out and
they
let the patent applications, to which I had granted them exclusive rights
lapse.

The technique is now public domain and works like a charm. Plot rho and mu
for metal discs as they slide down a chute!

These days I always have terms in my consulting contracts that give me
non-exclusive
rights to inventions or discoveries made in the processof performing
consulting work
for a client.

Wish I had thought about that when I was younger, could have had a lot of
royalty
checks that I just "gave away"...

 

[Tim Wescott]

Hi Rene,


There is a coin mech that already does the sorting to make sure the coin was
valid. If a coin makes it to the place I want to attach some sort of
sensor, it has already been validated. I just need to detect that it passes
through a small chute without physically touching it... That is why I was
thinking of something like a light/LED sensor/detector...

Thanks,

SA Dev

I'll assume that your coin sorter doesn't give you this signal, for some
valid reason.

A phototransistor and a LED would work, but have you considered debouncing
your mechanical switch? It's usually a good idea to "debounce" the
phototransistor/LED combo anyway so it's not like you're going to get out of
the work. I did a search on the keywords "switch" and "debounce" in
Altavista and got many useful references, so I won't bother on adding my own
half-baked discussion here.

As long as the coin isn't really energetically bouncing from your wire
contactor to the point where you wouldn't be able to distinguish a single
coin from a double coin you may just want to effectively use what you've
got.

 

[Active8]

I'll assume that your coin sorter doesn't give you this signal, for some
valid reason.

A phototransistor and a LED would work, but have you considered debouncing
your mechanical switch? It's usually a good idea to "debounce" the
phototransistor/LED combo anyway so it's not like you're going to get out of
the work. I did a search on the keywords "switch" and "debounce" in
Altavista and got many useful references, so I won't bother on adding my own
half-baked discussion here.

As long as the coin isn't really energetically bouncing from your wire
contactor to the point where you wouldn't be able to distinguish a single
coin from a double coin you may just want to effectively use what you've
got.

The ones I've seen just send the sized coin past a microswitch arm.
Passes slugs equally well, I suppose.

 

[SA Dev]

Tim,

A phototransistor and a LED would work, but have you considered debouncing
your mechanical switch? It's usually a good idea to "debounce" the
phototransistor/LED combo anyway so it's not like you're going to get out of
the work. I did a search on the keywords "switch" and "debounce" in
Altavista and got many useful references, so I won't bother on adding my own
half-baked discussion here.

Yes, maybe I can use the microswitch and debounce it. I'll search for some
debounce circuits and see if that might help.

Thanks to everyone for posting,

SA Dev

 

[Check It Out]

The ones that always intrigued me were the coin mechs that had weights to
balance the coins as they rolled down and sorting slots. Worked well until
they got dirty.

Electronic ones used several ring tank circuits, sometimes in combination
with photosensors to determine which coin was used. The "ring" count is
programmable, allowing them to learn coins or tokens.

Jim:

[snip]

Yep, I did some designs for a company called "Coin Accepters" *many*
years ago.

...Jim Thompson

[snip]

Hmmmm same here...

but I did designs for a company, now defunct, called "Electro-Vend"...

Now I wonder... "Coin Accepters" or "Slug Rejecters", which one is most
difficult?



All depends upon the viewpoint.

In my invention, I used two balanced bridges, each in an active bridge
detector
circuit, each using an inductor surrounding the coin chute, but oriented in
two
perpendicular directions.

One coil had windings parallel to the coin face, the other coil had windings
surrounding the chute and coin.

The first coil induced high circulating eddy currents and the bridge
unbalance
due to the excess eddy current resistance caused by the currents circulating
in the sample coin measured/indicated the electro-resistivity rho
as the coin passed by. The other perpendicular coil induced smaller eddy
currents
and measured mainly inductance and hence magnetic permeability mu as the
coin
passed by.

By simultaneously measuring both electro-resistivity rho and magnetic
permeability mu
on one known coin sample one could accurately determine the coin's size,
value, and
presence...

We built several prototypes and they worked very well... Electro-Vend
applied for
patents on my invention, but went under when their seed capital ran out and
they
let the patent applications, to which I had granted them exclusive rights
lapse.

The technique is now public domain and works like a charm. Plot rho and mu
for metal discs as they slide down a chute!

These days I always have terms in my consulting contracts that give me
non-exclusive
rights to inventions or discoveries made in the processof performing
consulting work
for a client.

Wish I had thought about that when I was younger, could have had a lot of
royalty
checks that I just "gave away"...

 

[Dave VanHorn]

The ones that always intrigued me were the coin mechs that had weights to
balance the coins as they rolled down and sorting slots. Worked well until
they got dirty.

They weren't supposed to be lubed either, but every so often, someone would
spray one full of WD-40 to "fix" it.. Fixed like a cat.