I see this one a lot,

People wondering why their current modes “aren’t working at all” on their multimeters. Well, chances are the fuse has been blown. Why? — Perhaps you tried to perform a parallel measurement in current mode, which would’ve caused a short.

However the point of this entry is not to point fingers, instead I’d like to remind you of the industry standard test for open fuses on multi-meters:

1. Put your DMM in Continuity mode, if it doesn’t have one just use the lowest Ohm range (In case it’s an auto-ranging DMM, just select Ohms)
2. Connect your red probe to the suspect banana jack. In this case the uA/mA input
3. If you get a low ohms reading, the fuse is fine. If you get an open circuit, it’s blown
4. Repeat step 2 for the “A” (Amps)  input and follow up with step 3.

Why it works

This circuit demonstrates how a reverse biased silicon diode can be used as a makeshift temperature sensor.

Note: If you can't find a 1 MOhm variable resistor or potentiometer simply try different fixed resistors, ranging from 1MOhm to 470K, 220K, etc.

The diode, when reverse biased, will present a certain leakage current that happens to be proportional to the junction temperature. This little current needs to be amplified, so we cascade three transistors in darlington configuration for maximum gain. The variable resistor allows us to set the overall “sensitivity” of the circuit. Without the transistors this small amount of current would be useless for us.

The small 10nF capacitor helps us obtain a certain hysteresis in the circuit, it may be removed if it’s effect is undesired.

A simple variation of this circuit would allow an LED bargraph display to indicate the temperature level. To achieve this we must create a voltage drop for each output LED, we can do this with regular silicon diodes. Then each LED would be driven by an NPN BJT with 1K base resistors.

Now, due to the high input impedance of this circuit you musn’t touch the sensor diode, likewise if you want to do remote sensing you must use a shielded cable. Failure to do so will introduce all sorts of noise into the base of the transistor rendering the circuit useless.

An even simpler version!

This version of the circuit involves only a 1n4148 diode, a high brightness LED and a resistor.

A few uAs of leakage will turn most high brightness LEDs on.

When you heat up the diode with a lighter, the leakage current is enough to turn on most modern LEDs producing visible light! — Of course, the temperatures required will most likely damage the diode in a very short period of time, however it’s one neat little experiment proving the concept at a bare minimum cost.

Hopefully you’ll be able to experiment with this circuit and come up with some useful variations!

Cheers.

What’s new:

Several packages were revised and new parts added, specifically two of the msp430 microcontrollers I use the most from the G series. And several ground related symbols. (supply symbols yet to come!)

You may visit the original post for a list of parts and download links.

Minor modifications:

• Several SMD footprints had their silkscreen redesigned with rounded corners and more accurate outlines.
• I added the package type and size at the bottom of each DIP IC footprint, for now it seems to be a good idea — we’ll see.

New parts:

This is my personal Eagle library, it has very few parts at the moment but it will grow as I work on different projects, so stick around if you want the latest version. You are free to use it for your personal projects. Contact me for details.

The devices currently in the library are:

• ICL8038
• LCD3510i
• LM4040
• LTC1144
• MAX4580
• MMBT3904
• PIC18F2520
• REF50XX ( REF5010, REF5020, REF5025, REF5030, REF5040, REF5045, REF5050 )
• TL431
• OPA209
• MSP430G2553
• MSP430G2231

Something to download

You can download the lib from here: eaglelib_gushh_v4.zip.

If you find any errors please let me know, however I have used this library for my own projects and so far I haven’t noticed any boo-boos. On the other hand I am not responsible for your own mistakes and cannot held accountable for any losses. Use it at your own risk

Enjoy.

It’s new and shiny, but…

After taking a look at the new feature-set for Eagle V6 I got quite excited, but then it hit me… Will they ever make this version available with a lite license? And which features will be cut out?

I’m not a fan of XML but it’s certainly a step into the right direction. The more you open your formats the wider the acceptance of your package will be, generally speaking.

Continue reading “Eagle V6 To spread wings” »