Creating a UserForm from an Excel Spreadsheet April 1, 2006
This is a work in progress, but it allows you to create a UserForm based on the cells in an Excel spreadsheet. The data can then be edited in the UserForm and copied back to the spreadsheet. The VBA code could use a few more features, but I thought I would post this as-is in case anybody wanted to pick it up from here. Please let me know if you improve on this.
File: userform-from-spreadsheet-2.xls
PCB Via Calculator March 12, 2006
This Javascript web calculator calculates the resistance, voltage drop, and power loss of printed circuit board vias. Note that vias are made out of plated copper which typically has a resistivity of 1.7E-6 to 2.2E-6 Ohm-cm. The calculator has an input box for the resistivity which defaults to 1.9E-6 Ohm-cm.
Updates:
May 22, 2006 - Added thermal resistance calculation.
January 19, 2007 - Minor Clarifications.
March 28, 2007 - Updated resistivity. See comment 12.
June 21, 2007 - Added estimated ampacity. See comment 17.
Inputs:
| Finished Hole Dia | ||
| Plating Thickness | ||
| Via Length |
Optional Inputs:
| Applied Current | Amps | |
| Plating Resistivity | Ohm-cm |
Electrical Results:
| Resistance | Ohms | |
| Voltage Drop | Volts | |
| Power Loss | Watts | |
| Estimated Ampacity | Amps |
Thermal Results:
| Thermal Resistance | Deg. C/Watt |
Notes:
Resistance = Resistivity*Length/Area
Area = pi*(Inner_dia + Plating_thk)*Plating_thk
Resistivity = 1.9E-6 Ohm-cm (plated copper)
(plated copper is much more resistive than pure copper)
Copper Thermal_Resistivity = 0.249 cm-K/W (at 300K)
Est_Ampacity [Amps] = k*(Temp_Rise [deg C])^b*(Area [mils^2])^c
For IPC-2221 external layers: k = 0.048, b = 0.44, c = 0.725
References:
[1] "Constructing Your Power Supply - Layout Considerations", by Robert Kollman
http://focus.ti.com/lit/ml/slup230/slup230.pdf
[2] "Current Carrying Capacity of Vias", by Doug Brooks and Dave Graves
http://www.ultracad.com/articles/viacurrents.pdf
Calculator Wish List March 3, 2006
If there is a calculator that you feel would be a good addition to this site, please add it to the comment section of this post and we’ll do what we can to implement them.
Creating UserForms Programmatically February 7, 2006
Creating UserForms Programmatically
and Handling Events with a User-Defined Class
This post contains an example Excel VBA file that demonstrates creating a UserForm programmatically and handling events with a user defined class. This is especially handy for creating forms with many similar controls. The file contains examples with Buttons, ComboBoxes, and TextBoxes. The figures below show the form with a button grid and the response of the event handler. Download the Excel file: UserFormProgEvents2.xls
Reference:
This is an extension of work found here:
http://www.j-walk.com/ss/excel/tips/tip44.htm
PCB Trace Width Calculator January 31, 2006
This Javascript web calculator calculates the trace width for printed circuit boards based on a curve fit to IPC-2221 (formerly IPC-D-275). Also see the via calculator.
New features:
- Results update as you type
- Several choices of units
- Units and other settings are saved between sessions
- Blog format allows user comments
Inputs:
| Current | Amps | |
| Thickness |
Optional Inputs:
| Temperature Rise | Deg | |
| Ambient Temperature | Deg | |
| Trace Length |
Results for Internal Layers:
| Required Trace Width | ||
| Resistance | Ohms | |
| Voltage Drop | Volts | |
| Power Loss | Watts |
Results for External Layers in Air:
| Required Trace Width | ||
| Resistance | Ohms | |
| Voltage Drop | Volts | |
| Power Loss | Watts |
Notes:
The trace width is calculated as follows:
First, the Area is calculated:
Area[mils^2] = (Current[Amps]/(k*(Temp_Rise[deg. C])^b))^(1/c)
Then, the Width is calculated:
Width[mils] = Area[mils^2]/(Thickness[oz]*1.378[mils/oz])
For IPC-2221 internal layers: k = 0.024, b = 0.44, c = 0.725
For IPC-2221 external layers: k = 0.048, b = 0.44, c = 0.725
where k, b, and c are constants resulting from curve fitting to the IPC-2221 curves
For geometry diagrams, click on the pictures below.
For frequently asked questions, see the comments.
PCB Trace Resistance Calculator January 24, 2006
This online web calculator finds the resistance of copper PCB traces (a.k.a. tracks) of given width, thickness, length, and temperature. It can also be used for copper bars (e.g. bus bars). Several choices of common units are available. Enter the Width and Thickness below. Optionally, enter the Temperature and Length, or just leave the default values. (To find the needed trace width based on current, see the PCB Trace Width Calculator.)
May 17, 2006 - Added (lateral) thermal resistance calculations.
January 18, 2007 - Clarified equations.
The Calculator
(more...)
Best Free Circuit Simulator January 21, 2006
I have been using LTspice (a.k.a. SwitcherCAD III) for about 3 years as my main circuit simulation tool and have been very happy with it. Linear Technology has generously made it available free on their web site, and it is full-featured, fast, and seems to converge very well. I’ll be posting some of my simulation tips and tricks, so I highly recommend that you download it and get familiar with it. They also have a great user’s group to help get you going.
Find Standard Resistor and Capacitor Values
This javascript calculator finds the closest standard resistor (or capacitor) value in each of the IEA series. Use this, and get rid of that tattered old standard decade resistance table taped to your cubicle and put a nice photo there instead!
| Desired Value: |
| IEA Series | Closest Value | Error |
| E6 | ||
| E12 | ||
| E24 | ||
| E48 | ||
| E96 | ||
| E192 |
Which IEA series applies to the various component types?
- E6: most capacitors, some inductors
- E12: some capacitors, 10% resistors
- E24: 5% resistors
- E48: 2% resistors
- E96: 1% resistors
- E192: 0.5%, 0.25%, 0.1% resistors
Health Calculator
This post includes an online calculator that calculates how many calories you burn per day and your Body Mass Index (BMI).
Calories/Day
Your Basal Metabolic Rate (BMR) is the calories needed for basic body function without any activity. Total Daily Energy Expenditure (TDEE) your BMR plus calories burned from activities. These can be helpful in planning food intake, diet, etc.
Body Mass Index (BMI)
The National Heart, Lung, and Blood Institute suggests the following:
- A BMI below 18.5 means you are underweight.
- A BMI of 18.5 to 24.9 is normal.
- A BMI of 25 to 29.9 is overweight.
- A BMI of over 30 indicates obesity.
The Calculator
(more...)
Dynamic Excel Chart Colors January 17, 2006
Did you ever want to have the colors of an Excel bar chart change dynamically with the values of the chart? The code below gives results like those shown below.
Just place this code (more…)
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