Driving circuit for Large 7 segment Display

Thread Starter

demnikgr

Joined Nov 9, 2019
6
Hello everybody, I could use some help with a project I 'm working on.
I have a up/down counter, to be specific its the Velleman kit K8035.
It 's working fine, but now I have to make it work with Large 7 segment display, KYX-40101AS.
Can anybody help with the circuit I need to drive those Big Display and make them work with the K8035 kit?
Thank You!
 

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djsfantasi

Joined Apr 11, 2010
5,704
Hello everybody, I could use some help with a project I 'm working on.
I have a up/down counter, to be specific its the Velleman kit K8035.
It 's working fine, but now I have to make it work with Large 7 segment display, KYX-40101AS.
Can anybody help with the circuit I need to drive those Big Display and make them work with the K8035 kit?
Thank You!
Sorry, I refuse to view PDFs anymore. My cell phone OS no longer displays PDFs unless you download them locally. Which #^*+ up my phone.

It is not a difficult problem. Based on the specs of what the device CAN operate and the corresponding specs of the large display unit, I’d just build a driver for the obvious higher current. A transistor driver or MOSFET driver.
 

dl324

Joined Mar 30, 2015
9,143
Welcome to AAC!
Can anybody help with the circuit I need to drive those Big Display and make them work with the K8035 kit?
I think you're going to have problems.

The kit displays are on a 5V supply.
1573591963825.png
The datasheet for the large LEDs shows 5 LEDs in series for each segment.
1573591996112.png
The datasheet gives forward voltage information, but it's unclear if it's for each diode or for 5 in series. I'd assume the former.
1573592062916.png

Could you confirm whether the segments will turn on with the stated voltage under VF?
 

Thread Starter

demnikgr

Joined Nov 9, 2019
6
Sorry, I refuse to view PDFs anymore. My cell phone OS no longer displays PDFs unless you download them locally. Which #^*+ up my phone.

It is not a difficult problem. Based on the specs of what the device CAN operate and the corresponding specs of the large display unit, I’d just build a driver for the obvious higher current. A transistor driver or MOSFET driver.
Dear djfantasi thanks for the fast reply.
can you see photos? I tried the ULN 2803A without success... I not sure how to do the circuit and the components ...
 

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Thread Starter

demnikgr

Joined Nov 9, 2019
6
Welcome to AAC!
I think you're going to have problems.

The kit displays are on a 5V supply.
View attachment 191256
The datasheet for the large LEDs shows 5 LEDs in series for each segment.
View attachment 191258
The datasheet gives forward voltage information, but it's unclear if it's for each diode or for 5 in series. I'd assume the former.
View attachment 191260

Could you confirm whether the segments will turn on with the stated voltage under VF?
Hi dl324, thanks for replying!
Well the Voltage I tried and is working is 12V to light the segments and I used a 2,2k resistor on +v...
 

djsfantasi

Joined Apr 11, 2010
5,704
First, you need to determine from the display kit specs the current draw of a single segment. Call that Is. Then, calculate the total maximum current draw by multiplying the segment draw by 7. Call it It

The transistor at the top of the second schematic must be able to handle this amount of current. The resistors R9-R12 must be resized to supply 1/10th of that current to the transistor base. Call 1/10th of the current I’d. To calculate the resistance value, you need the voltage supplied by the pins DY1-DY4. Call that Vd. Then the resistor is equal to the next size greater than Vd/Id.

Secondly, you may need a driver for the segments. If the segment outputs outputs of the circuit cant supply a current of Is to the segments, you’ll need a BJT/MOSFET driver for them. Note that a simple driver will invert the signal, so use a second BJT/MOSFET in front of each segment driver.

MOSFETs may be simpler than BJT transistors, especially for the segment drivers, because instead of calculating base resistors, you can likely use 10K resistors as pull-ups or pull-downs on the drain as needed.
 

Thread Starter

demnikgr

Joined Nov 9, 2019
6
First, you need to determine from the display kit specs the current draw of a single segment. Call that Is. Then, calculate the total maximum current draw by multiplying the segment draw by 7. Call it It

The transistor at the top of the second schematic must be able to handle this amount of current. The resistors R9-R12 must be resized to supply 1/10th of that current to the transistor base. Call 1/10th of the current I’d. To calculate the resistance value, you need the voltage supplied by the pins DY1-DY4. Call that Vd. Then the resistor is equal to the next size greater than Vd/Id.

Secondly, you may need a driver for the segments. If the segment outputs outputs of the circuit cant supply a current of Is to the segments, you’ll need a BJT/MOSFET driver for them. Note that a simple driver will invert the signal, so use a second BJT/MOSFET in front of each segment driver.

MOSFETs may be simpler than BJT transistors, especially for the segment drivers, because instead of calculating base resistors, you can likely use 10K resistors as pull-ups or pull-downs on the drain as needed.
dear djfantasi,
I not sure I can follow you... the specs of the big Displays are in the next photo.. I 'm sending and the specs of the kits displays SA39-11EWA..
 

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dl324

Joined Mar 30, 2015
9,143
Well the Voltage I tried and is working is 12V to light the segments and I used a 2,2k resistor on +v...
What is the voltage drop on the segments?

It just occurred to me that the kit uses common anode displays. The displays you want to use are common cathode. That will require additional circuitry to do the required inversion.
 

Thread Starter

demnikgr

Joined Nov 9, 2019
6
What is the voltage drop on the segments?

It just occurred to me that the kit uses common anode displays. The displays you want to use are common cathode. That will require additional circuitry to do the required inversion.
everything is common anode..
 

eetech00

Joined Jun 8, 2013
1,726
Welcome to AAC!
I think you're going to have problems.

The kit displays are on a 5V supply.
View attachment 191256
The datasheet for the large LEDs shows 5 LEDs in series for each segment.
View attachment 191258
The datasheet gives forward voltage information, but it's unclear if it's for each diode or for 5 in series. I'd assume the former.
View attachment 191260

Could you confirm whether the segments will turn on with the stated voltage under VF?
Judging from the TS statement that the LED's lit with 12v, the specs must reflect a single LED in a 5-LED segment.
However, TS also stated a "2.2k" limiting resistor which seems way too high. Should be more like 100 ohms for a 5 LED-series segment.

eT
 
Last edited:

djsfantasi

Joined Apr 11, 2010
5,704
Judging from the TS statement that the LED's lit with 12v, the specs must reflect a single LED in a 5-LED segment.
However, TS also stated a "2.2k" limiting resistor which seems way too high. Should be more like 100 ohms for a 5 LED-series segment.

eT
You have made some important observations. I didn’t see it in the spec, but Knowing the current draw of a segment is critical to know. Secondly, the voltage drop across a segment is just as critical b.
 
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