Push to make-555-4026b-7 seg

[John Murdock]

1) This is a simply circuit that I have duplicated from an online image. The function of this circuit is to count the amount of coins that are dropped and making contact with the switch, I know the switch needs a debouncing circuit which has been made and done but I believe other inputs could be better and more sensetive such as piezo transducers but I could use the variable resistor to change the sensetivity of the switch. POINT: Better inputs than the push to make switch?

2)Currently I understand how the 7 segment display works but not the rest. previously I experimented with using 4 switches as the inputs to make binary code and display number but of course with the needed function this is impractical. POINT: How does the 4026b work in co operation with the 555? why is the 555 there? how does this work by sending a single signal while previously it needed 4?

Still young and not very advanced however I do understand the concepts of electronics and what not. Any help would be much obliged. Thanks.

 

[DerStrom8]

Hello,

Personally I'd push for an optical sensor--An infrared transmitter one one side of the slot the coin passes through, and an infrared phototransistor on the other side. Use the phototransistor in place of the switch. I don't believe that will require debouncing, and it's much more reliable.

What happens if you put more than 9 coins in?

Matt

 

[John Murdock]

Thanks for the advice I'am just going to draw that up.

to answer your question:

 

[John Murdock]

Hello,

Personally I'd push for an optical sensor--An infrared transmitter one one side of the slot the coin passes through, and an infrared phototransistor on the other side. Use the phototransistor in place of the switch. I don't believe that will require debouncing, and it's much more reliable.

What happens if you put more than 9 coins in?

Matt

-I've been told before that the 555 is useless or what not : is that correct?
-Since I do not have an infrared transmitter could I use an opto isolater which I do have?

 

[DerStrom8]

Thanks for the advice I'am just going to draw that up.

to answer your question:

View attachment 97730

-I've been told before that the 555 is useless or what not : is that correct?

That schematic is a huge mess. Please try to redraw it with fewer crossing wires, and with the order of its operation flowing left-to-right (i.e first LED driver on the left, second to the right of that, and third to the right of that). Also put your displays next to each other with the 100s digit on the left, 10s digit in the middle, and 1s digit on the right.

-Since I do not have an infrared transmitter could I use an opto isolater which I do have?

You cannot use an opto-isolator, as the LED and receiver are enclosed in the package and the coin can't pass between them. The point of the transmitter/receiver is so that when the beam is blocked, it means a coin has passed and it can increment the counter.

I'm glad to see you fixed the switch. Your first schematic was wrong, your second one is right--The switch should be connecting pin 2 to ground when pressed.

You do not need the 555 timer though. The switch will act as a clock source itself, so it can be fed directly into the clock input of the 4026. However, the clock is active high. This means that to increment, you need the input to jump HIGH, then low again. In order for this to work, your switch would need to connect the clock input to V+ when pressed. If you use a phototransistor your logic will be inverted, so you would need to invert it back. When no coin is blocking the beam, current will be allowed to pass between the collector and emitter. When the beam is broken the transistor will not conduct. This is not what you want. You'll need to invert the signal back by connecting the collector of the phototransistor to a pullup resistor (pulling it up to V+). Connect the emitter directly to ground. Your output is from the collector of the phototransistor. When there is no coin the beam is present, and the phototransistor is conducting. This pulls OUT down to ground, giving you a 0 for an output. When a coin is dropped and the beam is broken, for a fraction of a second the phototransistor does not conduct, and the output is fed through the pullup resistor, and the output is HIGH. This is your clock signal for the 4026.

 

[audioguru]

The 555 monostable de-bounces the switch. Without the 555 when you push the switch it might bounce many times which is counted. You time it so it prevents switch bounces but allows as many coins that you want in a short time duration.

 

[DerStrom8]

The 555 monostable de-bounces the switch. Without the 555 when you push the switch it might bounce many times which is counted. You time it so it prevents switch bounces but allows as many coins that you want in a short time duration.

Woops! Didn't even think that it was being used for debouncing....

If you use optical sensors though you won't need the 555 -- There won't really be any bounce to speak of.

 

[AnalogKid]

-I've been told before that the 555 is useless or what not : is that correct?

No. On all electronics fora (the plural of forum) there are two groups of crazies - those who think the 555 is the only answer to just about everything, and those who think any chip over 3 years old is ancient garbage. Tracking which group is less rational keeps the rest of us entertained. Note that 40 *years* after its introduction the 555 still is selling over 1 billion pieces per year worldwide - hardly useless. But I digress...

In your circuit the 555 is configured as a retriggerable monostable, one form of a debouncing circuit. With proper attention to detail, it can be eliminated while still having the input switch debounced. Even if you go with an optical interruptor, a little debouncing on its output will catch the few remaining errors.

Your counter circuit needs a pull-down resistor on the reset line. Also, the 4026 is not really built to drive displays directly. The datasheet has three display application circuits, and all of them have external drivers of some kind. You can drive one display directly, but it will not be very bright and should have 7 current limiting resistor, one per segment. That's 21 additional resistors on your schematic.

Another approach to the counter is the CD4553 / MC14553. This is a 3-digit counter with a display multiplexer built in. It needs one decoder/driver and one set of 7 resistors, so the net circuit body count is lower.

And finally, the Intersil ICM7217 (now made by Maxim), a 4-digit counter complete with decoding and display driving built in. It is the all-in-one solution, a bit of overkill with presets and comparators that you can ignore.

ak

 

[John Murdock]

Your counter circuit needs a pull-down resistor on the reset line. Also, the 4026 is not really built to drive displays directly. The datasheet has three display application circuits, and all of them have external drivers of some kind. You can drive one display directly, but it will not be very bright and should have 7 current limiting resistor, one per segment. That's 21 additional resistors on your schematic.

Another approach to the counter is the CD4553 / MC14553. This is a 3-digit counter with a display multiplexer built in. It needs one decoder/driver and one set of 7 resistors, so the net circuit body count is lower.

And finally, the Intersil ICM7217 (now made by Maxim), a 4-digit counter complete with decoding and display driving built in. It is the all-in-one solution, a bit of overkill with presets and comparators that you can ignore.

ak

The 555 can be kept or I could use a debouncing circuit which I has been done in a previous post. In regards to the resistors you are right 21 resistors is a lot and will be a pain when it comes to the pcb.

Now left with the others the LCM7217 is actually very interesting and a great potential learning curve but once again 28 pins on a pcb is not going to be the easiest thing; a battle for another day. Out of the potential other two ICs the cd4553 seems to be more commonly used and would definitely be a better option to use.


one issue, surely instead of using the mc14553 one could use 3 4026bs as this post claims:
https://www.electro-tech-online.com/threads/using-3-cd4026s-as-an-alternative-to-an-mc14553.122757/

 

[AnalogKid]

*Total* pin count is one way to evaluate the total effort in bringing a design through to production, but don't let the size of one component throw you. The 7217 requires NO segment current limit resistors and NO digit drive transistors. In some ways it takes the fun out of your circuit, but for you it is more fully integrated than a microcontroller programmed for your application. 61 pins vs. 28...

ak

 

[John Murdock]

Another approach to the counter is the CD4553 / MC14553. This is a 3-digit counter with a display multiplexer built in. It needs one decoder/driver and one set of 7 resistors, so the net circuit body count is lower.

And finally, the Intersil ICM7217 (now made by Maxim), a 4-digit counter complete with decoding and display driving built in. It is the all-in-one solution, a bit of overkill with presets and comparators that you can ignore.

ak

By multiplixer do you mean that all the 3 digit counters will only need 7 inputs?

For a decoder/driver does the 4511 sound good?

based on this circuit: https://www.kitsrus.com/pdf/k1.pdf the all in one 3 digit ''multiplexer'' only has 7 inputs, so the multiplexing reduces the amount of pins needed?

 

[John Murdock]

*Total* pin count is one way to evaluate the total effort in bringing a design through to production, but don't let the size of one component throw you. The 7217 requires NO segment current limit resistors and NO digit drive transistors. In some ways it takes the fun out of your circuit, but for you it is more fully integrated than a microcontroller programmed for your application. 61 pins vs. 28...

ak

In essence I can't disagree with that statement.

 

[AnalogKid]

By multiplixer do you mean that all the 3 digit counters will only need 7 inputs?
based on this circuit: https://www.kitsrus.com/pdf/k1.pdf the all in one 3 digit ''multiplexer'' only has 7 inputs, so the multiplexing reduces the amount of pins needed?

If by "inputs" you mean outputs, then - yes.

Display multiplexing is reasonably straightforward. Each digit has 7 segments. Tie all of the segments of each location together. Segment a output to digit 1 segment a to digit 2 segment a to digit3 segment a. Output b to digit 1 segment b to digit 2 segment b to digit 3 segment b. etc. Then each digit's common (anode or cathode) is tied to a driver that is controlled by the multiplexer. To display 123, the system activates the segments for the numeral 1 and activates the driver for digit 1, then turns off digit 1, changes to the segments for the numeral 2, and turns on digit 2, etc. It does this so quickly that your eye and brain see all 3 digits all the time. There is only one set of 7-segment outputs and current limiting resistors, and the current is higher because each display is on only 1/3 of the time. The 7217 goes farther by integrating the segment current limiters and digit driver transistors on the chip.

ak

 

[John Murdock]

If by "inputs" you mean outputs, then - yes.

ak

That is correct.

Currently on the software that I use (circuit wizard) non of the cd4553, MC14553 or the 7217 are in the components section any recommendation on software that I could use and download?

 

[AnalogKid]

Nope. It would take a very comprehensive built-in library to include the 45xx CMOS parts, and no one will have the Intersil timers. The majority of the parts in my design libraries came from me adding them.

However, most layout programs have a manual or on-the-fly mode where you can do a layout from scratch with no netlist or schematic. They usually have the standard IC packages and a way to connect two pins, so you can draw your circuit manually. Of course you lose the design rule checking and might mis-connect things, so you have to be careful.

ak

 

[John Murdock]

Nope. It would take a very comprehensive built-in library to include the 45xx CMOS parts, and no one will have the Intersil timers. The majority of the parts in my design libraries came from me adding them.

However, most layout programs have a manual or on-the-fly mode where you can do a layout from scratch with no netlist or schematic. They usually have the standard IC packages and a way to connect two pins, so you can draw your circuit manually. Of course you lose the design rule checking and might mis-connect things, so you have to be careful.

ak

Right, was just thinking about that, that makes life a lot more complicated but this will simply have to do.