3 digit 7-segment display

[wolf9545]

Sorry if this has been asked before, went through a few pages from a search and didn't see anything, and sorry if it is in the wrong section.

I want to build the lightning detector project, Lightning Detectors, and one of the add-on boards I want to do is a counter. I will take the pulse line and feed it into a 4026 chip, 4000 series CMOS Logic ICs, and that would go to a 7-segment display. I understand that to be able to display the 3 digits so I can count to 999 I have to take the output from pin 5 from the first chip and connect that to pin 1 of the next chip and so forth. Then I would just connect each 4026 to a 7-segment display to display the count. Each 7-segment display would be separate making it harder to mount them all next to each other.

How would I use one of these, BC56-12GWA Kingbright LED Displays? It is three 7-segment display all put together into one package so it would make it easier to mount to a case. Does each 7-segment still have it's own input for the led's?

 

[Reloadron]

Your choice of display I don't believe will work with the counter scheme you have in mind. Give this link a read to better understand what I am talking about. Also, the chips used in the link I have not seen in over 20 years but you will get the idea of how the common cathodes in the display are multiplexed. Your best bet for what you want to do with the parts you have would likely be three discreet seven segment displays.

Ron

 

[Brevor]

You may want to look into using a 4543 IC and a 4553 IC to do the counting, instead of 3 4029 IC's and 3 4511 IC's. It will save parts, 2 IC's instead of 6.

 

[Reloadron]

Here is the data sheet for the MC14553 which was mentioned in my previous link and Brevor suggest. I was not aware that chip was still available. Surprise on that note. As Brevor points out, it would get the parts count way down and would drive the display you linked to. The data sheet shows some circuits.

Ron

 

[wolf9545]

You may want to look into using a 4543 IC and a 4553 IC to do the counting, instead of 3 4029 IC's and 3 4511 IC's. It will save parts, 2 IC's instead of 6.

So if I understand it correctly I would use one 4543 and a 4553 to drive one 3-digit display and display a count? I was originally looking at the 4026 chip because it does both the BCD and led driver circuit in one but I would need a 4026 for each 7-segment display.

Is there a good free software to simulate the circuit so I know it works?

 

[Reloadron]

So if I understand it correctly I would use one 4543 and a 4553 to drive one 3-digit display and display a count? I was originally looking at the 4026 chip because it does both the BCD and led driver circuit in one but I would need a 4026 for each 7-segment display.

Is there a good free software to simulate the circuit so I know it works?

Yes, if you use the 4026 decade counter you would need to cascade 3 chips. Each chip would drive a discrete seven segment display. The 4026 will not drive the seven segment display you linked to doing what you wish it to do. You would need 3 each 4026 chips and 3 each discrete seven segment displays.

The display you linked to is designed to be used with the chips that were linked to earlier. The counter chip "strobes" each display as the data for that display is present.

The first link I posted shows exactly how to build the circuit and yes, it will work as it is a very common counter design. As to software? I am not sure what would give you a good simulation.

Ron

 

[Brevor]

Looking at Ron's first link it shows you can use a 4511 in place of a 4543, a 4511 should be easier to find. I used these in a counter design about 30 years ago so my memorys a bit foggy, but I do recall it worked well.

 

[wolf9545]

After looking at the datasheets for 4543 & 4553 I think I might stick with the 4026 chip. The datasheet for the 4026, https://focus.ti.com/lit/ds/symlink/cd4026b.pdf, states that it has schmitt triggered inputs so I don't need to add another circuit. It has both the counter and 7-segment driver built into one along with outputting a low mA so I don't need any resistors between the chip and the 7-segment. I understand I still will need three separate 7-segments and three separate 4026 chips but that should be it; no extra resistors or other items.

The only thing I am not too sure is if I will need to put a resistor before the input of the first 4026 to limit the current on the "pulse" line from the lightning detector circuit. Thank you all for your help.

 

[crutschow]

After looking at the datasheets for 4543 & 4553 I think I might stick with the 4026 chip. The datasheet for the 4026, https://www.electro-tech-online.com/custompdfs/2011/05/cd4026b.pdf, states that it has schmitt triggered inputs so I don't need to add another circuit. It has both the counter and 7-segment driver built into one along with outputting a low mA so I don't need any resistors between the chip and the 7-segment. I understand I still will need three separate 7-segments and three separate 4026 chips but that should be it; no extra resistors or other items.

If you depend upon the 4026 output current limit to determine the LED current then there can be significant differences between chips in how much current they will provide which would cause uneven brightness between numbers. It's better to use a resistor to establish the current through each LED segment.

 

[wolf9545]

Why would there be an un-even current on the 7-segment leds? I thought since each chip would be receiving 5V then each chip would output the same amount of current to the 7-segment?

 

[crutschow]

Why would there be an un-even current on the 7-segment leds? I thought since each chip would be receiving 5V then each chip would output the same amount of current to the 7-segment?

Making assumptions in the operation of ICs often leads to errors -- you need to read the data sheet. You are using the chip to limit the current and its limit is not a controlled value. It depends upon the manufacturing variations of each batch of chips manufactured. The data sheet states that there is a 2:1 variation between the minimum and typical output current and there is no max. limit given.

So what do you think the current output value will be?

 

[wolf9545]

Sorry for the late reply but when I started this post I didn't have a job but now I do; less time to work on this but more money to spend.

I think I might just go with the multiplexed setup. The one with the 4511 and the 4553 chips because I will only use two IC's. The main problem is trying to figure out how to wire it all on a pcb board. I know what connects to where, I'm using the supplied article in post #2. Where my problem lies is, I am using "Design Spark" to design the pcb board so I can use the toner transfer method to etch the board myself. I would like to keep it to a one sided board if possible just so I don't have to play the "is everything lined up on both sides before I etch" game. Does anyone know if there is a IC multiplexer that does the job of both the 4511 and the 4553 in one package? This way the pulse would come in, from the lightning strike, and then get outputted to the multiplexed 7 segment display.

 

[colin55]

You can use a single micro such as a PIC chip to create the 3 digit display.

You did not say what you wanted to count but the pic chip will do all that for you too.

 

[wolf9545]

Sorry. What I want to count is the lightning strikes from this lightning detector; http://www.techlib.com/electronics/lightning.html. If you look at the schematic you will see a pulses output which would connect into the clock input on a IC chip. I really don't want to use a PIC chip because I don't have anything to program one with. Thank you though.