Having trouble with logic IC's, MC14555B

Thread Starter

The_Real_Tony_Clement

Joined Apr 4, 2022
1
Hi as the title says I can't get either the MC 14555B Decoder.
I have a bigger issue with a 74LS93 counter but I forgot to take a picture of the 74LS93 so I will post that tomorrow.

I separated the Counter and the Decoder to test them individually, they still don't work. I am really unfamiliar with IC's so any advice is appreciated.

I tried to hook up the MC14555 to two buttons to replicate the high and low logic of the counter. The power into the breadboard is 5V limited to 0.6A.
Initially the first Led turns on
First button press: turns on the two middle LED's, and the last led turns off.
The second button does nothing. I have tried to wire the B input pin to the power lines but it also does nothing.

Swapping the VSS and VDD does nothing.
I am confused as to which should be positive and which should be negative. According to google Vdd is the drain and the Vss is the supply but the datasheet implies the opposite.

1649444757855.png
 

MrChips

Joined Oct 2, 2009
26,133
You have a number of problems:

1) Do not mix 74LSxx chips with MC14xxx or CD4xxx chips.
2) You cannot test inputs with just a push-button alone. Basically, you cannot leave an input pin with nothing connected. Use a resistor (1k-10kΩ) to pull-up or pull-down the input pin when the push-button is not pressed.
3) When testing a counter IC you cannot use a push-button alone. The push-button must be debounced otherwise you will be sending multiple clock pulses with one button-press.
4) Try to colour code your jumper wires i.e. be consistent, e.g. red is +Vcc and black is GND.
 

dl324

Joined Mar 30, 2015
14,480
Welcome to AAC!
Swapping the VSS and VDD does nothing.
Don't do that. Connecting power backwards will put a diode across the power supply and the device can be destroyed.
I am confused as to which should be positive and which should be negative. According to google Vdd is the drain and the Vss is the supply but the datasheet implies the opposite.
As the datasheet indicates, Vdd is the positive supply:
1649452250591.png
1649452606541.png

When the switches are opened, you're allowing the A and B inputs to float. Since you have the switches wired to the supply, you need to put pull down resistors on the inputs for correct operation.

Since you're a novice, you shouldn't mix 74LS with CD4xxx logic. TTL isn't guaranteed to provide logic levels required by CMOS. If you want to mix 74LS and CMOS, you need to use 74HCT which are CMOS devices that have input voltages that are compatible with TTL outputs. You can use pull up resistors on the 74LS outputs, but that defeats the advantages of having totem pole outputs.
 

eetech00

Joined Jun 8, 2013
3,161
You havn't really stated the led sequence but I think this is the operation you are trying to achieve.
The CD4555B is the same as the MC14555B
BTW- The cmos output can only drive about 3mA with a 5v supply.

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dl324

Joined Mar 30, 2015
14,480
I can't get either the MC 14555B Decoder
Something to consider.

The logo and markings on your part look suspicious (i.e. counterfeit) to me:
1649523209156.png

Here are some examples I have:
motOnLogo.jpg
The bottom two were bought on eBay before counterfeiting had become such a problem. The rest were acquired from reputable sources in the 70's-80's.

This is what the stylized M should look like:
1649523388499.png
 

dl324

Joined Mar 30, 2015
14,480
More things to consider.

CD4xxx logic wasn't designed to sink or source much current, with a few exceptions like CD4049/50:
1649621727099.png
1649621679436.png
Unless you are operating at 15V, you can't expect to get 3mA. At 15V, you circuit would require more like 13mA.

A proper schematic makes what you're not doing correctly obvious:
1649621950549.png

Since you're a novice, you should get in the habit of drawing schematics. The only time we need to see a breadboard is if we suspect that you're not wiring things correctly.

To your credit, you didn't use those long pre-made jumpers or have a lot of unnecessary white space. I suggest that you start forming the leads with some needle nose pliers and not count on the package to prevent you from damaging components.
1649622456363.png
 
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