# CD4541B One Shot Timer

#### WARDEVIL_UFO

Joined Nov 16, 2010
41
For my class Lab, we are specifically instructed to construct a 1 minute one-shot pulse, and a 5 minute one shot pulse using a CD4541B for both of these time periods. I have found a thread where eetech00 kindly fixed one of the files for the OP. I am using the files found on that thread and the fixed version of the IC.

Ever since I added the CD4541B into my schematic LTspice has been kind of bugged. I had to remove the "step" out of ".tran 66 step" to get an error message about "Can't find steady State" removed. But even still, once I halt the simulation, I can't seem to use my probes any longer. The probes come back if I use the scissors to cut the CD4541B from the schematic. Here is a picture of my circuit. I will attach the files that I am using for CD4541B. I watched a couple videos on how to import symbols and models into LTspice.

#### Attachments

• 1.5 KB Views: 4
• 954 bytes Views: 3
• 441.6 KB Views: 2

#### MrChips

Joined Oct 2, 2009
30,928
On a side note, it is unrealistic to expect a CMOS RC circuit to have a time constant longer than a few seconds. The R and C values have to be very large. Large C values (greater than 10μF) are not very stable and reliable for timing purposes.

#### WARDEVIL_UFO

Joined Nov 16, 2010
41
The time constant that I used in my original post is tau = R*C = (5000 ohm)*(47 uF) = 0.235 seconds. Setting pin A = HIGH, and B = Low, should create a multiplier of 2^8= 256. 256*.235 = 60.16 seconds.

If using above 10 uF is a issue for accurate timing, I suppose I could have the same 0.235 second time constant by choosing C= 4.7 uF instead of 47 uF, and then choosing resistors that are 50k.
TAU = R*C = (50k)*(47 uF) = 0.235 seconds. When this is multiplied 256 times, that should also be 60.16 senconds like above.

#### MrChips

Joined Oct 2, 2009
30,928
The time constant that I used in my original post is tau = R*C = (5000 ohm)*(47 uF) = 0.235 seconds. Setting pin A = HIGH, and B = Low, should create a multiplier of 2^8= 256. 256*.235 = 60.16 seconds.

If using above 10 uF is a issue for accurate timing, I suppose I could have the same 0.235 second time constant by choosing C= 4.7 uF instead of 47 uF, and then choosing resistors that are 50k.
TAU = R*C = (50k)*(47 uF) = 0.235 seconds. When this is multiplied 256 times, that should also be 60.16 senconds like above.
There is a limit as to how high R can be. Keep R below 1MΩ. For stability, C should be 0.1μF or lower, non-electrolytic.

CD4541B is a special case.

It has a 16-stage binary counter with four possible scale values, 256, 1024, 8192, 65536. Pick a scale that allows you to use the highest clock frequency.

#### WARDEVIL_UFO

Joined Nov 16, 2010
41
I have modified C and R within the parameters there Mr. Chips advised. (Thank you Mr. Chips; Tip appreciated for when I actually put this together and build it!) R=73.6k and C= 0.1uF. I had to set pins A&B = 0, for a a power of N=13, and thus a multiplier of 8192.
The pulse width should be TIME = 2^13*R*C= 8192*(73.6k)*(0.1u) = 60.29 seconds

I still have the same problems attempting to run the simulation and making measurements as before. While my real-world apparatus would likely have been affected by the issues Mr. Chips brought up, I don't think that it is the cause of my simulation hanging.

#### Attachments

• 1.5 KB Views: 2
• 954 bytes Views: 1
• 3.1 KB Views: 2
• 441.6 KB Views: 1

#### MrChips

Joined Oct 2, 2009
30,928
Sorry, I don’t have LTspice. I rarely use simulators, I prefer to see real silicon working.

#### eetech00

Joined Jun 8, 2013
4,004
Use .tran "startup" option, or IC=0 as cap attribute, to get the oscillator going.
Either one will start the oscillator, but produce different timings.

The model is not a very good model.