Are there dangers to humans from PCB/Circuit Corrosion?

A buddy of mine has a bunch of old electronics that were his fathers that were in storage for a long time, and some of them look pretty bad.

Some of the items look similar to what is shown in this picture:

With blue spots, nasty oil looking brown spots, and similar brown damage/build up on chips and parts.

I am curious how dangerous stuff like this could be for human handling, as well as being in his attic breathing while around this stuff? Are there any worries one should have?

NOTE: I'm not sure if this is a question better suited to biology/chemistry due to the nature of interaction with humans/chemicals, but figured since this is about electrical components it would best be suited here.

7segmentdisplay - Can a laser display numbers like an LCD 7 segment display?

Possible Duplicate:
Is there a way to convert a 7 segment display to be displayed by a laser beam?

I am a 12 year old child with a growing interest in electronics. I want to have a laser project numbers like a 7 segment display. Is there a way to hook a 7 segment display up to a laser to have the laser display the numbers onto a flat surface?

The design needs to be as compact as possible. Do you know if maybe there is an electronic converter or way that can be used to hook it up in place of the 7 segment display? Like this:

Binary for the 7 segment display -> ??Mystery part described above??? -> Laser display module.

I just started electronics a few days ago, I've got some grasp on the basic stuff, but I could really use some help here. I have a very limited amount of resources available and needed to ask people who know what they're doing.

rf - What is the purpose of holes on edge of the PCB?

Here is a photo of one of Texas Instrument's RF EVMs.

Please pay attention to edge of the PCB that has multiple tiny holes. I marked 3 of them with a red circle on the photo.

What is the purpose/benefit of them? The edges are V cut, is it something to do with it? Or if it is kind of performance improvement, then how do you determine what size of the hole to use and the distance between the holes?

EDIT:

Here is the gerber view of the board (not the same edge), as I can see, they are just holes (not vias)

Answer

Those are vias. They are connecting that one piece of ground plane to another one on another layer.

It may be done for increasing current carrying ability, thermal transfer, EMI reduction, and any number of other reasons.

Given that it's an RF board it's most likely to help control unwanted EMI.

When you have two ground planes, and high frequency, different points of the ground planes will be at different voltages, with respect to each other. 0V is never 0V throughout an entire system, but varies due to the inductance of the traces.

Two traces with different high frequency signals in them make a nice dipole antenna. By strapping those two traces (ground planes) together you are effectively nullifying much of those voltage differences, and turning it back from an antenna to just a ground plane. And of course the effect is most pronounced at the edges of the planes, so that's where you want most of your vias. You notice there are also plenty of vias throughout the whole ground plane in an attempt to keep the potentials as even as possible.

brushless dc motor - BLDC BEMF not right

I am trying to build my own ESC (brushless DC controller) and I managed to get the motor running starting from a ramp to a steady PWM duty Cycle and Commutation period and these are the BEMF waveforms that I see. My question is, where is the "zero crossing event" and why is it different (somehow inverted) from the regular BEMF waveforms displayed on various application notes?

Please refer to the images below:

Here-in, it is almost impossible to detect '0' crossing. Also, in my scheme I am PWMing the upper MOSFETS, with the lower ones being used/made high during relevant commutations.

Answer

This business of starting from scratch is exceedingly difficult. Something about your waveforms looks wrong, but with phase descriptions how can we know exactly?

I make a guess that you are commutating wrong, perhaps as well pwming the low side. Generally with correct commutation the zero cross part of the commutation shows a rise at pwm hits rather than a fall as yours are showing. Also, it seems odd that the low is riding up around 1-2 volts during certain commutation periods.

I have added some waveforms scope shots from a working esc. Although there appear to be issues, this is driving the motor. Note the rise from zero evident at the zero crossing period.

Also, don't forget that sampling has to be synced with your pwm.

My start with BLDC began with this kit. Can't you find a similar kit, so that you have a known good reference point? If your or your boss cannot afford this kit.. Then this is the price of learning perhaps?

microcontroller - Help find data sheet for micro-controller?

I found a packet of 10 micro-controller in my brother's electronics stuff. It reads "Atmel ATMEGA168A-PU".

I looked at Atmel's website but could not find any such product. I need it's data sheet to know that it is capable of ? I would like to play with it.

Answer

Here you go. Datasheet for the ATmega48A; ATmega48PA; ATmega88A; ATmega88PA; ATmega168A; ATmega168PA; ATmega328; ATmega328P - Atmel 8-bit Microcontroller with 4/8/16/32KBytes InSystem Programmable Flash

This microcontroller can be used to make your home-grown Arduino clone, among other things. The DIP part lends itself to making the Really Bare Bones Board quite well.

voltage - How to modify DS1307 RTC to use 3.3V for Raspberry Pi?

I bought DS1307 RTC but it is 5V so it can't be connected to the Pi. I know it can be modified to use 3.3V by removing 2 resistors. This sensor is different than the adafruit kit so I am not sure which resistors to remove. It also has 2 sets of pins. What are the extra pins for and which should I use and which pins do I remove?

Here is the image of the RTC:

Here's the datasheet for the DS1307 RTC.

Answer

In order to make it work with 3.3v lines you have to remove the two pull-up resistors connected between SCL->5v and SDA->5v and then use 3.3v pull-up resistors on the MCU side (unless they are already integrated).

In the board I see four 332 (3k3) resistors which are definitely the pull-ups, just locate which two connect to the relevant I2C pads, it shouldn't be difficult with an ohmmeter.

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Your RTC connection pins are on the right side (P1 header)

I finally managed to find a schematic here

The pull-ups for the RTC I2C lines are R2 and R3

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According to the schematic and the comments in the reference site, the SCL and SDA lines of both headers are interconnected.
There is also a DS pin (one in each side, interconnected), it is currently unused but is intended for the 1wire signal of a DS18B20 temperature sensor which can be added on the board in the three pads located in the left top side.

baudrate - Does Bluetooth range increase with lower baud rate?

I am using two Bluetooth dongles for an Arduino project of mine. I am only sending a single int over the connection so it does not need to have a high baud rate.

If I use a baud rate of 1200 will I be able to have more range than if I were to use something such as 115200?

Answer

In my experience, radio modules usually have 2 different baud rates:

• UART baud rate is the baud rate for communicating to microcontroller on the board. Usually, it's adjustable.


• Over-the-air baud rate is the baud rate for communicating via Bluetooth. It's usually fixed.

I've searched through the user manual and datasheet for RN-41, which is the Bluetooth module inside the dongle. I didn't find any indication that over-the-air baud rate is adjustable in this module.

So, I doubt that you will get more range if you configure the baud rate down to 1200.