Electronic – Ghosting on 7 segment display

displayeeprommultiplexer

I have an EEPROM (AT28C64B) multiplexed and connected to 3 seven segment displays,

I did so using a tutorial online from ben eater https://www.youtube.com/watch?v=dLh1n2dErzE&t=300s

enter image description here

Sorry for the bad quality photo

Here's my setup, from left to right, the ICs I'm using, 555 timer connecting in Astable mode, SN74LS112 Dual JK flip flop, SN74LS139 Demultiplexer and the 7 segment display I'm using is called a SC05-11EWA (I only have two but a third is in the post)

I've had a problem with ghosting on the 7 segment displays and I'm not quite sure how to fix it, I have exhausted google, to no avail so I hope someone can help.

If you need further info feel free to comment.

Thanks, Patrick

(edit)
enter image description here
Here's a schematic I made using EasyEDA, sorry about the cluster it's my second time making a schematic.

Best Answer

You have a race condition happening.

When the counter is changing the data presented from the EPROM will be indeterminate and as such LEDs will light at random for a short period.

As such you need to disable the drivers while the data is changing.

In this case you can use the clock signal from the 555 to control the output enable (OE, Pin 22) of the EEPROM such that it only drives the LEDs during the second half of the clock cycle.

Since you are using a negative edge triggered flip-flop for your counter, you need to invert the output from the 555 to feed that enable pin.

As others have mentioned, you also need some current limiting resistors in the LED lines. You are also asking a bit much of the 139 to power all segments, a transistor or MOSFET drive for the common would be prudent.

schematic

simulate this circuit – Schematic created using CircuitLab

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