Clocked D-Latch

Continuing with the D-latch we can make it a be more useful by making a dedicated PCB for it which dramatically reduces the size compared to the last one we made.

So to start with we need to make the logic gate diagram

This should look like the previous D-latch we made. But in this version we have added Preset and Clear, which will allow us to set the out put to high or low in start up or if we wanted we could over right the existing data (Q) with high or low.

Now that we have the logic diagram we need to make the schematic.

Here we have the layout of all the BYT's for the D-latch, and on the top left I have added a Buffered LED, so that we can see the state of the latch. You may notice that some of the BJT's are missing a base resistor, but after some testing I figured out that in some cases when a BJT is controlled by another gate, the collector resistor of the gate acts a base resistor for the following BJT. This save time and components.

Now we need to lay out the board.

On the left is the front and the right is the back.

I tried to optimize the layout so that assembly was as easy as possible, I did this by placing duplicate parts next to each other as well as describing the components instead of giving the components reference ie R2 and Q5 as for me that was not as helpful.

Assembly was quite strait forward there were just a couple of resistors that jumped arround.

Next is putting it to use.

Here we have the D-latch with the data input coming from the red switch, we have enable coming from the Rising edge trigger, which is set off by the Switch which is connected to an SR latch (to stop the bouncing), we also have an Buffered LED to display the state of the SR latch. (I'll have the schematics of the Edge trigger and the SR latch at the bottom)

So it works by entering the value you want into the red switch, and when you are satisfied with your choice you switch the switch up which sets off the rising edge trigger which enables the D-latch which saves the Data value and displays it on its LED. as we can see below.

Now that value is safe until the switch is turned off and on again, and the cycle repeats.

Here is the Rising edge trigger.

At first I only used 3 NOT gates as you can see but after testing with this configuration the delay was not great enough, so I had to add 2 more NOT gates.

And this is what the BJT layout looks like.

Here is the Switched SR latch

Its nothing special just a regular NOR SR latch with the inputs for S R being the output of the Three position switch (ON OFF ON)