I've previously completed a project where I built a display using some 4" 7 segment LEDs that are controlled using some 4511's. I interfaced the 4511's from a printer port relay board that I had purchased a while ago (Kit 74).
I used 4 of the relays to control the A-D lines on the 4511's and then used 3 of the relays to control each individual LE on the 4511's. This allowed me to write out a 3 digit number using a program on the computer.
I wrote the number by writing the binary digit to all 4511's and unlatching then relatching an individual 4511 that corresponded to the number I wanted to change.
My problem is that my new computer doesn't have a printer port. I purchased a usb board from Elexol and instead of getting the relay board that I could have just swapped in I opted for the UNL2803 board because I wanted to try to eliminate the noise and delay of the relays.
Just to clarify I'm a computer programmer, not an EE so I'm struggling.
The old way I controlled the LE on the 4511 by something like this...
Ground ---- 10K resistor ---- wire to the LE on 4511 ---- wire to the relay N/C pole
9V ---- wire to the relay Common pole
So when the relay was open the LE would be low because it was connected to the ground, allowing the digit to be changed. When the relay was closed the LE would be high because of the 10k resistor (electricity takes the path of least resistance right?), latching the current digit so a different 4511 could be changed.
On the new version I want to replace the "switching" of the relay with the ULN2803. If I understand that board correctly when the input on the ULN2803 is turned on it grounds the corresponding output of the ULN2803. I'm having a hard time grasping how to make the LE on the 4511 high when the output line of the ULN2803 is not activated.
Can somebody help me fit this into my project?
I'll try to draw up a better diagram and attach it.
I used 4 of the relays to control the A-D lines on the 4511's and then used 3 of the relays to control each individual LE on the 4511's. This allowed me to write out a 3 digit number using a program on the computer.
I wrote the number by writing the binary digit to all 4511's and unlatching then relatching an individual 4511 that corresponded to the number I wanted to change.
My problem is that my new computer doesn't have a printer port. I purchased a usb board from Elexol and instead of getting the relay board that I could have just swapped in I opted for the UNL2803 board because I wanted to try to eliminate the noise and delay of the relays.
Just to clarify I'm a computer programmer, not an EE so I'm struggling.
The old way I controlled the LE on the 4511 by something like this...
Ground ---- 10K resistor ---- wire to the LE on 4511 ---- wire to the relay N/C pole
9V ---- wire to the relay Common pole
So when the relay was open the LE would be low because it was connected to the ground, allowing the digit to be changed. When the relay was closed the LE would be high because of the 10k resistor (electricity takes the path of least resistance right?), latching the current digit so a different 4511 could be changed.
On the new version I want to replace the "switching" of the relay with the ULN2803. If I understand that board correctly when the input on the ULN2803 is turned on it grounds the corresponding output of the ULN2803. I'm having a hard time grasping how to make the LE on the 4511 high when the output line of the ULN2803 is not activated.
Can somebody help me fit this into my project?
I'll try to draw up a better diagram and attach it.
