# Combining 74HC74 & 555 Integrated Circuits

After working with some basic 74HC74 and 555 circuits, it was time to get fancy. I replaced one of the button triggers from my 74HC74 circuit with a 555 timer delay.

Then I replaced the other button with a 555 timer delay as well.

What do you think happens if I swap out the 22 μF capacitors for 4.7 μF? Remember the capacitor charge time formula from the 555 post? Multiply the capacitance (farads) by the resistance (ohms) to get the time. I’m still using the same 100 K ohm resistors.

$t = RC$

$100000 * 0.0000047 = 0.47$

So the delay decreases from 2.2 seconds to 0.47.

There is really no point in the 74HC74 here. You can connect two 555s to each other for a similar result. The video shows a double 555 circuit with 3 different timings, where I swap the capacitors from 22 μF to 4.7 μF and then 1 μF (delay of 0.1 second).

Are there any other circuits I should try with the 74HC74 and/or 555?

# Using a 555 Integrated Circuit

555 Pins

I posted about the 74HC74 flip-flop on Saturday. For the same project I’m going to use that IC for, I’ll probably use a 555 timer. It’s often referred to as one of the most useful ICs you can get. I’ve never used the 555 either, so I wired up some simple demos using it. In order to show two common timing uses, I’ve created similar circuits each triggered by the same power source and button.

The circuit on the left shows a delay off timer and the one on the right shows a delay on timer. Notice when power is connected (or the button is used as a reset) that the red LED turns on right away and turns off after a few seconds. Just the opposite, the white LED is off when the timer is reset and turns on after a few seconds.

The length of the delays is determined by the capacitor and resistor used with the 555. I’m using an Adafruit Feather to provide 3.3 volts to the circuits with a 22 μF capacitor and 100 K ohm resistor. Using the capacitor charge time formula to multiply the capacitance (farads) by the resistance (ohms), it’s easy to get the time.

$t = RC$

$t = 100000 * 0.000022$

Comes out to 2.2 seconds. To change the time delay all you have to do is use a different capacitor and/or resistor.

Here is a simplified wiring setup because it’s hard to see how everything is connected in the video.

Also check out Combining 74HC74 & 555 Integrated Circuits.

# Using a 74HC74 Integrated Circuit

74HC74 Pins

I received some advice to use a 74HC74 flip-flop for a project idea I’ve had. I’ve never used an integrated circuit so I thought a good first step was to put together a very simple demo I could hack around with it. This IC is big enough it actually provides two flip-flops, one on each side as you can see from the pin diagram on the right. Both sides work the same, but are completely independent other than sharing power and ground. I’m only using the first side for this example.

As I press the buttons connected to CLR and PRE, you can see the outputs (Q and not Q) alternate. I’ve set the data (D) and clock (CLK) pins to ground. The truth table for the 74HC74 comes in handy to understand what’s going on.

Here is a simplified wiring setup because it’s hard to see how everything is connected in the video.

Also check out Combining 74HC74 & 555 Integrated Circuits.

# Home Improvements

Over the past couple of weeks I’ve been busy with home improvements. First my Dad came down for a weekend and we did some odds and ends, but the big project was installing a ceiling fan/light in my bedroom. Previously there wasn’t a light in the room and with it being a pretty large room it was hard to see with just a corner lamp in the room.

Neither my Dad or I are electricians or have any experience, but we got the project done and learned a lot along the way. The original configuration had a switch at the door of the room which controlled the top plug of two outlets. In the end, this switch draws power and is connected to another switch inside my closet (which is right by my bed). So now I can turn the light/fan on when walking in/out the room and also when jumping into bed. All of the plugs on the outlets are always hot now and no longer controlled by a switch. The entire project too a whole day, 4 trips to Home Depot, and who knows how many trips up into the attic. It sure does make the room look nice though.

On Sunday I started tearing down wallpaper in the closet and sink area of my bedroom. The original plan was to do both this are and the bathroom at the same time. After over 5 hours on the first room, I decided to turn them into two separate projects because not having good lighting and a mirror by the sink really sucks! Monday I moved all of my clothes out of the closet (the wallpaper stopped right before the closet area of the room) and took down all of the shelving and clothes hanging bars, then scrubbed any remaining glue from the walls and wiped them down. Last night I sanded and patched up all of the holes and marks on the walls. Hopefully tonight I can sand my patch jobs, wipe down the walls, put on some Kilz where it’s needed, and get the painting done. That would leave Thursday night to put everything back together in the room, move in my clothes, and finally unpack some boxes which hadn’t been done since moving in.

Every project turns out to be much harder and more time consuming than you originally think, but of course I then add on to them as well. I don’t like to do shit half-ass, so I do the extra work. I figure if I’m working on it, might as well do things right the first time and spend the extra time.

Owning a home is really a lot of work, but it feels great to accomplish something and know you are adding value to your home at the same time as you’re making it look great.

# How To Wire a 3-way Switch

Want two electrical switches to control the same light or outlet? Check out a diagram before you do anything. This would have saved my Dad and I a couple of hours on Saturday.