Archive for March, 2012

Netlist with cadence 16.3 / Allegro in windows 7 - Error initializing COM property pages

March 16th, 2012

Did you get an error trying to generate a netlist from Cadence 16.3 Orcad for the Allegro PCB Editor 16.3. In some enterprise edition you get an error that pops up saying

Error initializing COM property pages

and says some "wrong pointer" etc.

Here is a quick solution for it. Take a look at the screen shot

Basically, you need to run the Orcad as an Administrator. You need to do it only the first time.



Watts Hour and Ampere Hour

March 10th, 2012

The capacity of a battery life is specified either in Ampere Hour or in Watts Hour. Let us understand the two terms and the inter relation between them.

The Ampere Hour is more intuitive term for expressing the battery life. If a battery is specified at 20 Ampere hour then the implication is simple - A 20 Ampere hour battery life will last for 20 hours if it draws 1 Ampere of current. It will last for 10 hours if it draws 2 Ampere of current. Simple ?

The problem with the Ampere hour specification is that it does not specify the Voltage at the battery. Let us say you have two batteries. Both the batteries A and B has a Ampere Hour rating of 10 Ampere Hour. However, Battery A is at 3.6 Volts while the Battery B is at 7.2 Volts. Now if you draw 1 Ampere of current from both the batteries, both will last 10 hours. But the Battery B is delivering 1 Ampere at 7.2 Volts while the battery A is delivering it at only 3.6 Volts. I strictly technical terms we say that battery B has double the capacity of the battery A.

This is where the Watt hours come in play. If a battery is rated 20 Watt hours, it will mean that it will last for 20 hours if 1 Watt power is drawn from it. Now watt is defined at the product of the Volt ( at the battery) and Ampere ( drawn from the battery).

In the previous example, the 20 Ampere Hour 7.2 Volt battery would be rated as 1440 Watt Hour while the 20 Ampere Hour 3.6 Volt battery would be rated at 720 Watt Hour.

You can use the battery life calculator to calculate the life of a battery. This calculator just calculates the battery life if you know the Ampere Hour rating and the current drawn from the battery.


RMS Formula ( Root Mean Square Formula)

March 2nd, 2012

The rms value of a set of n values for (x1, x2, .....xn) is given by

This formula is valid for a set of n discrete values. If you have a continuous variable, you can use Calculus to derive the formula for various common waveforms, for example the sinusoidal waveform.

For example if a is the amplitude of a sinusoidal waveform the vrms is given by

You can use the following calculator to calculate the rms value , if you know the peak to peak value

rms to peak to peak calculator

Probably you cam here searching for the formula for the Root Mean Square or, rms for the short. Before we give out the formula and the explanation, let us find the need of a root mean square.

A company Xing Hua, makes nuts and bolts and supplies it to various companies in US and Europe. The company makes a strict record of all the quality procedure that it adapts.

The nuts and bolts had their dimensions measured with automatic tools after they are finished and recorded in a spread sheet. That is a great !!! Said the CEO when he visited the shop and looked into the quality procedure adopted by them. The QA engineer then calculated the mean of the internal diameter of the nuts and found that the average of the dimension of is very close to the required dimension. The required dimension was 2.050 mm while their average dimension was 2.051 mm. Pretty close.

A few months later the order that came from Japan for an automobile company was rejected. The company went bankrupt.


Had the QA engineer measured the rms average in place or regular average, they could have caught the fault much earlier saving the company from bankruptcy.

You may have now understood the story now. Let us say we want to hit an average dia of 2.50 mm. If one piece has dia of 1.5 mm and second one has a dia of 3.5 mm, the average is still 2.50 mm, but both are useless.

So we define root mean square.

We take the difference. The differences are as follows

For 3.5 mm the difference is +1.0 mm
For 1.5 mm the difference in -1.0 mm

The average is 0
But the root mean square is sqrt ( (1)^2 + (-1)^2) /2) = 1.0

This is 1.0 mm - non trivial value.

So coming back to the rms formula. Here is the formula for the RMS

The rms value of a set of n values for (x1, x2, .....xn) is given by

Other Resources

- If you are, however looking at the rms value corresponding to a waveform, you may like to check vrms to vpeak to peek calculator