Circuit & Component Check

For the PIC16F627, it reads

The only references in electrical specs I can see are:

and

mA, may cause latch-up.

to the MCLR pin rather

But I'm pulling MCLR *up*, to stop it resetting, aren't I?! :-\

Cool, that'll save me a few components then! So if it's configured as an input, and pull-ups are enabled, I don't need any resistors, but just leave it unconnected, or connected directly to ground for a high/low respectively?

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Danny

LOL! And they published this guys book! ;)

Maybe you can clear up a few terms I keep hearing, but keep ignoring cos I don't full understand!

Base / Collector / Emitter - I don't completely understand.. Is the collector always +ve and the emitter grounded/-ve?

Sink / Drain - These seem to be used in describing which way things are connected... Used in the datasheets quite a bit too, such as "input/open drain output"

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Danny

I did mean RB0 & RB1, correct.

100 Ohm sounds more like it, I've got a few different LEDs here, and the resistors have worked out as 120 and 160. *However*, I did connect a 1K today, since it's the lowest I have till my stuff arrives, and the LED is more than bright enough. Maybe he can get 1K resistors cheaper than 100 Ohms ;-)

LOL! I can't believe so many of you noticed that so quickly! Guess I'll double check before copying any examples from that book ;o)

The base, collector and emitter (B, C, E) are the three terminals of a bipolar transistor. The base and collector are positive with respect to the emitter of an NPN transistor. The reverse is true of a PNP transistor.

The emitter of an NPN transistor is not always connected to ground.

Gate, drain and source are the terminals of a field effect transistor. They are in, a limited sense, equivalent to base, collector and emitter.

A "current sink" is something into which current flows; a "current source" is something out of which current flows. An output "sinks" current when it pulls low; and "sources" current when it pulls high.

An "open drain" output can only pull low. The pull-up transistor is disabled in this mode. It goes tri-state (i.e. floating, high-Z, open circuit) for logic 1. The external circuitry determines the pin's potential: it must not be allowed to float.

The bipolar equivalent of "open drain" is an "open collector" output.

Well, I've answered your specific questions. I could go on, but this is a MASSIVE subject. I recommend the book "The Art of Electronics" by Horowitz and Hill if you fancy some good arm chair / bed time reading on the subject. It's informal, readable and not at all stuffy or dry.

Correct. You don't need external pull-up resistors on your inputs if you enable the internal pull-up facility.

At £50, I think I'll see if the Library have it first ;-)

Ta!

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Danny

In this case, they are both 100 Ohm. There is fundamentally no difference between the two LEDs that would justify two different resistor values unless you want different brightnesses.

I actually thought it was excellent that you showed this. I started in electronics from a design in a book that did not work all that well, although, the components were probably about the right values and the transistor orienation was correct. This helps a lot because mainly people assume that if you are not familiar with electronics and you are following a schematic from a book, then if it fails, it must be your fault. You now learned what I have: Examine every component. Ask what it is doing there and why the values for each component are what they are. I am more and more finding published schematics that I could make improvements on.

Dominic

Is the emitter ever connected and actually running at a voltage that is higher than the collector? Is this described in the Horowitz book?

Dominic

No, not the emitter of an NPN transistor: the minimum collector-emitter voltage is about 0.2V when the transistor is saturated.

The H+H book covers this in detail.

Try bookpool. They had it for $50 US. Who knows now, though, with the dollar having 'issues'?

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

$53... with $25 shipping to the UK... Even with the exchange rate in my favour, that's gotta be over £40!

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Danny

Danny,

I just bought this book at Ebay for 27 brittish pounds with shipping within USA... There were a number of copies of this book being sold there. Be cautioned there is another, related book, maybe a lab manual, etc, that sells for about half the price. If you go the auction route, pay close attention to what people are wanting for shipping and handling, and stick with people with a good record from previous deals.

Here is the one I got: Ebay #4515997432

There is another auction right now, even lower price. Just type in the name of the book and you should find several examples, such as: Item 4516689114

Dominic

Yep, the Student Manual - I noticed that right away :)

I'll take a look, though I don't usually buy things more than about £20 from ebay - there are too many scammers (ebay don't make a big enough deal of feedback - some people with hundreds of "good feedback"s are from small £1 auctions with their mates) and ebay seem to be useless at sorting out mishaps! :-(

Thanks everyone - picked my bits up today (postman had claimed he couldn't deliver them and left them at the sorting office!), and put it together. All works brilliantly! :)

I tried yesterday with some odd components lying around, but only had an NPN transistor, no MOSFET, which resulted in my motor going fast and slow, instead of fast and off!!

Now I just need wheels and a chassis! ;)

Ta,

--
Danny

It is always a good idea to review the data sheet if you can find one:

--
John Popelish

Study the data sheets and come back with anything you see that doesn't make sense to you.

--
John Popelish

Danny, it will be great to see how this progresses. I am interested in the reason why the effect on speed is occurring. It sounds like a problem I am encountering with the 2N3055 NPN power transistor. I do not find conditions under which it actually shuts off and I do not understand why. I do know the basic calculation strategies using beta to determine Ib from a pre-determined Ic, etc. It is maybe noteworthy that some of these inductor circuits (speakers, transformers, motors, etc) have variable current draw, so this must mean that Ic will vary. If one clamps the Vbe and Ib with a fixed voltage and resistance, respectively, I presume that beta changes. I am quite curious how each of these parameters effects the others. At least in the case of the

2N3055, it has both low frequency 0.8 MHz, and I suspect slow rise and fall times and also relatively low beta (between 20 and 70). I suspect this obligates a very narrow dynamic range. Compare, for instance to a BD139 with a beta around 160 and frequency of 250 Mhz. Very different. I suspect the 2N3055 is leaky, but I lack good proof. It came as a surprise that I could run such inductor circuits a lot better with much lower power NPNs than the 2N3055. One of the most reliable was a BF658, which is small signal 1 Watt, Ic 0.12 Amp.

It is also frustrating that the specifications often do not tell what kind of NPN transistor. I have seen the 2N3055 called a Darlington, and I have seen internal schematics that clearly show that it is not. I suspect the latter, and nonetheless, this transistor has not been real popular with me, despite its massive power rating. I think it is the low beta (and leakage?) that has made working with it a challenge.

Dominic

I still don't fully understand the differences between all these different types of transistors/FETs... Since all works fine with the MOSFET (ZVN4206A), I assumed the transistor was just "amplifying" or something. A low from my chip seems to vary between 0V and -0.04 or so, so maybe this is by design - dunno! The resistor I was using was an BC108A.

--
Danny

I still don't fully understand the differences between all these different types of transistors/FETs... Since all works fine with the MOSFET (ZVN4206A), I assumed the transistor was just "amplifying" or something. A low from my chip seems to vary between 0V and -0.04 or so, so maybe this is by design - dunno! The resistor I was using was an BC108A.

--
Danny