Specifications?

Other Hardware General Electronics
1

I'm trying to understand the GP1A57HR in my photo-interrupter.
The specs
http://www.datasheetcatalog.org/datasheet/Sharp/mXrttzx.pdf
The parameters-column in the data-table 'Absolute Maximum Ratings' is split into
Input
Output

Output has a parameter "Supply Voltage", symbol Vcc. Is this just a confusing way to present information? If not, where do I supply voltage to an output?

Input has a parameter "Reverse Voltage", symbol Vr. Now, THAT is a usefull info for one like me that wires components upside down. The specs however seems to address professionals and not newbies. Seriously, .. the input [should be +6V and] can survive -6V, right?

Output seems not to represent the output-signal comming from the sensor as "Output current", symbol Io, is 50 mA. I conclude this in respect for my experience, that my setup-output cannot turn a LED on.

50% of the info in 'Absolute Maximum Ratings' deals with temperature and power-dissipation. That's usefull information if you've bought a boiler or sausage-fryer.

I've obviously got it all wrong. I don't in particular think of this component, but on specifications in general. I find Input and Output fairly well defined and intuitive so, .. what's the secret?

2

It's confusing, until you realise that "input" refers to the light source (infra-red LED), and "output" refers to the sensor (photo-transistor or photo-diode).

A photo-interruptor is basically two devices, a light source, which is the input to the device, and the sensor, which can be thought of as an open-collector output on a logic gate for example.

3

Thank you majenko,

I had been looking at the photo interrupter-specs, picked the mark on the sensor-part and googled to see it's particular specs. Didn't think of output/input the way you suggest, and it makes some difference!

No shortcut to learning your lessons ;o/

4

You usually don't need to study all of the specs... I guess the trick is to know what's important for your application and to just have general "feel" for what's normal and safe... The ATmega spec sheet is over 400 pages, and I probably haven't read one percent of it! When I'm unsure of something, I'll look it up.

If I'm using a 7805 voltage regulator to power a couple of low-power chips, I don't worry about the 7805 specs... If I'm working with something-k Ohm resistors (or higher) at 5V I don't worry about the power, voltage, or current ratings for the resistor. If Im getting down around 100 Ohms, then I'll calculate power dissipation for the resistor.

Output seems not to represent the output-signal comming from the sensor as "Output current", symbol Io, is 50 mA. I conclude this in respect for my experience, that my setup-output cannot turn a LED on.

A typical LED requires about 20mA, so powering an LED would be fine.

50% of the info in 'Absolute Maximum Ratings' deals with temperature and power-dissipation. That's usefull information if you've bought a boiler or sausage-fryer.

There's a reason for the power specs... As you may know, power is calculated as Voltage x Current. Under normal operation as a switch, the output transistor either is switched-on with current through it and nearly zero voltage across it, or it's switched off with voltage across it but nearly zero current through it. Under either of those conditions output-power is essentialy zero and we don't have to worry about it.

However... What happens if the light path gets partially-blocked and the thing turns "half-on"? Now, we have voltage and current at the same time and we are dissipating power. If we have happen to have a situation where we have the maximum current (50mA) and the maximum voltage (17V), at the same time, we are dissipating 850mW. We we have exceeded the maximum ratings and the thing might burn-up (or otherwise fail).

As far as temperature.... Temperature is related to power and it's the total temperature that's important. Thet means the heat generated internally by the device from the power dissipation plus the external ambient temperature. Your circuit/device might work fine in a normal room-temperature environment, but it might burn-out if you use it in a non-air conditioned environment in Arizona in the summer. :wink: But again, this is not something I'd worry about when the thing is operating "normally" as a switch.

5

DVDdoug,
That was a nice post.
It's so frustrating to be so close to all the electronic goodies and just miss a little detail and know exactly too little. My first specs were for a stepper .. in chinese.
I have a handful of photo-interrupters and I can do without some .. I often feel better off without the specs and then 'try by error'. My setup worked before I popped this post .. and I realize now that a particular resistor on the test-circuit is a pull-up, so I do come out a little wiser.
I've started looking at a Hall sensor .. with plenty of info not strictly targeted at professionals. Now, thats a walk in the park (so far).
Thanks

6

RSGB produces a "Handbook" similar to the ARRL handbook Both are in the beginning Basic Electronics training manuals. The first 6 - 10 chapters are devoted to basics for people with no knowledge of electronics... When I began to seriously study electronics the ARRL handbook (1949) and me starting in 1959 was my guide and helper for several years. I still use both the RSGB (Radio Society of Great Britain) and ARRL books today... nearly 49 years and the books, both are highly relevant... At Least the first 4 chapters... I set myself a goal of reading 10 pages a night during my study time (I was 13 then) I never made that goal... it took me about 2 weeks to finish the book and I never looked back at my decision. Your abilities in this field are directly tied to your willingness to seriously dedicate some time to studying the Basics First and then moving up. None of it is difficult and secondary school math 2 years is ALL the math you need (Basic Algebra is necessary and Basic Trigonometry will help for AC circuitry). Your success in any subject is directly proportional to the amount of work you put into the subject... No More and No Less.
It's not hard stuff to learn but learn it you must if you have any serious desire to succeed. I did and I retired a Happy Man with a very diverse knowledge set...

Doc

7

Morning, Doctor Edison,

"Your abilities in this field are directly tied to your willingness to seriously dedicate some time to studying the Basics First and then moving up"

I keep telling people this. It beats me why I want to escape it myself.
My own field is somewhere in natural science, and I used to say that mastering it is a matter of learning it's language. That seems appropriate to remind myself of. I got Daren Ashby's 'Electrical Engineering 101' and love it for the clear analogies he draws to simple mechanics.
I'm not particularly dedicated, but I did get challenged when I wanted to use a scrap motor from an old printer. I was convinced that it was an easy fix, but I grew wiser. Knowing that most mechanics are controlled by electronics I decided that time spent on it would not be wasted. Discovering Arduino was /the/ revelation that has turned all the hard stuff into a treasure trove of goodies.

8

The Hardest to do Well, The Most Rewarding Intellectually and Least Often Practiced let alone Accomplished.
I have been fortunate I have had a Book either in my hand or close enough to grab for years... Now If I could
Only keep from reading junk... Dirk Pitt novels for 2 weeks.... Eccch But that is the Problem when one is a little Manic

Doc

9

[warning: off topic]
Hi Doc;

"... Dirk Pitt novels for 2 weeks.... "

Everyone has professional challenges .. I assume that you are mellowing in on yours ;o). If not, I can provide you with one (I got to read your post on measuring humidity). As a geologist [of education, never worked as such] I miss geophysical hand-tools to support me in the field. I'm not sure what physical properties to home in on, but one example comes to my mind: Some prospectors will use a flame on a rock and evaluate it's color to get information on contents. .. naa, electromagnetic spectral sensing is fine, but it could well be way too pricy ...
lessee ..