Would like some help with a schematic

[joe61]

I'm working on a schematic for a pcb I'd like to try. I'm looking for something like the attached picture, only with a prototyping area as well. I'm not very good at this and I hope I'm not embarrassing myself too much, but I'm getting tired of soldering boards like this together, and then having to debug my solder joints etc.

I think I have the power supply part more or less ok. I did it with reference to Dave Cook's "Intermediate Robot Building", chapter on power supplies.

I don't know how to draw the connections tying in the ATtiny84, power supply ISP header, etc. I don't have the headers in yet, etc. If someone would loan me a clue I'd really appreciate it.

Thanks

Joe

-- Edit --
I added the Eagle .sch file in case that helps

[Soeren]

Hi,

I think I have the power supply part more or less ok. I did it with reference to Dave Cook's "Intermediate Robot Building", chapter on power supplies.

Link?
The supply will never work as it stands - Ask yourself "what is the purpose of Q1 and how does it work".

I don't know how to draw the connections tying in the ATtiny84, power supply ISP header, etc. I don't have the headers in yet, etc. If someone would loan me a clue I'd really appreciate it.

I'll loan you a clue (if you promise to give it back ), but could you specify the exact components that you want to have on the board and how you want it wired?
(A link to something you have used or...).

-- Edit --
I added the Eagle .sch file in case that helps

I'll be drawing it in version 4.16 as every version from v5 is very low on contrast, so gives me a headache to use (from eye strain).
You can open it in a newer version, but not the other way around.


If anybody have a link to Eagle version 4.60 I'd really like to see if that one still has a higher contrast than the newer versions.

[joe61]

Link?

The only link I have is about the book, but doesn't show that chapter: http://www.robotroom.com/IRB.html. I don't think he has it on the web cause he wants you to buy the book :-)

The supply will never work as it stands - Ask yourself "what is the purpose of Q1 and how does it work".

I thought it was a power MOSFET that I put there for protection against someone (me) plugging the battery in backwards. My understanding is that it will conduct if the gate has a lower voltage than the drain. I intended to connect the gate to ground, and the drain to 6V, so it will conduct. The book says that this being the case, if the battery is plugged in backwards, the gate will have a higher voltage than the drain, so it won't conduct.

Am I misunderstanding that, or did I just get it wrong on the schematic?

I'll loan you a clue (if you promise to give it back ), but could you specify the exact components that you want to have on the board and how you want it wired?
(A link to something you have used or...).

This is the first time I've tried this (with the transistor) so I don't have anything to point to. Previously I've done very simple power supplies, like the one in the Sparkfun tutorial (http://www.sparkfun.com/tutorials/57). I'm just trying to learn something new this time.

What I'm hoping to accomplish is to have some pcbs I can use for projects where I'll be using an ATtiny84. I'd like to have a clean power source, be able to program the chip on the board, and have headers I can plug servos or whatever into.

I'll be drawing it in version 4.16 as every version from v5 is very low on contrast, so gives me a headache to use (from eye strain).
You can open it in a newer version, but not the other way around.

No problem here. Appreciate the help. Sounds like I need it more than I thought.

Joe

[Soeren]

Hi,

The only link I have is about the book, but doesn't show that chapter: http://www.robotroom.com/IRB.html. I don't think he has it on the web cause he wants you to buy the book :-)

Yeah, David Crook doesn't wanna show you much of what's in his book until after payment. Just remember that he's not an engineer, so you should keep a sceptical perspective on whatever schematic he presents.

You could scan or draw the pieces in question and post only that. It's very hard to speculate or advice on a schematic that you haven't seen.

Or, I could just make up a supply unit for you.

I thought it was a power MOSFET that I put there for protection against someone (me) plugging the battery in backwards. My understanding is that it will conduct if the gate has a lower voltage than the drain. I intended to connect the gate to ground, and the drain to 6V, so it will conduct. The book says that this being the case, if the battery is plugged in backwards, the gate will have a higher voltage than the drain, so it won't conduct.

Am I misunderstanding that, or did I just get it wrong on the schematic?

Ah, so that's what you wanted to do.
You have chosen a bipolar transistor, not a MOSFET and you'd need a logic level type if you want it to be better than a simple diode.
Personally, I would place it ahead of the voltage regulator (protecting that as well) and I would add a resistor between the gate and ground.

What I'm hoping to accomplish is to have some pcbs I can use for projects where I'll be using an ATtiny84. I'd like to have a clean power source, be able to program the chip on the board, and have headers I can plug servos or whatever into.

Sure, but what schematic have you used for making them on matrix board?
And what are your plans for the prototype area? (overall size/pad types)
(Just need to get an idea of how you want it all connected up).

[joe61]

Sure, but what schematic have you used for making them on matrix board?
And what are your plans for the prototype area? (overall size/pad types)
(Just need to get an idea of how you want it all connected up).

I didn't use a schematic. This is the first one I've tried to do. I just knew what I wanted to wind up with and soldered wires to make that happen. I'll try to come up with some kind of picture tomorrow. I think I can borrow a machine with Visio on it and maybe use that. If not I'll just draw it out and scan it.

Thanks

Joe

[Soeren]

I didn't use a schematic. This is the first one I've tried to do. I just knew what I wanted to wind up with and soldered wires to make that happen. I'll try to come up with some kind of picture tomorrow. I think I can borrow a machine with Visio on it and maybe use that. If not I'll just draw it out and scan it.

OK, I studied your matrix board photo, so I assume you just want each pin brought out to headers and a strip of +5V and ground each side as well?

Do you want the female headers nearest the chip as in your photo?

I'll see if I can find where the programming headers go on the '84 (I haven't used Atmel chips for about a decade myself).

No need to draw anything if the above is what you want, but I need to know how large you want the proto area to be and how you want it connected.

Are you planning on single or double sided PCB?

[joe61]

OK, I studied your matrix board photo, so I assume you just want each pin brought out to headers and a strip of +5V and ground each side as well?

Do you want the female headers nearest the chip as in your photo?

Yes to all the above.

I'll see if I can find where the programming headers go on the '84 (I haven't used Atmel chips for about a decade myself).

VCC is pin 1
GND is pin 14
Reset is pin 4
MOSI is pin 7
MISO is pin 8
SCK is pin 9

No need to draw anything if the above is what you want, but I need to know how large you want the proto area to be and how you want it connected.

I'm looking for a final size of 5 x 3 inches. I assume that the PCB will make the existing stuff more compact, so I was going to use whatever's left for the prototyping area.

Are you planning on single or double sided PCB?

Dunno, I was going to let Eagle figure that out.

Man I'm starting to feel really ignorant :-(

Thanks

Joe

[billhowl]

Here are the Circuit from that book, you got it wrong, the MOSFET is at the front not the back of the circuit.

[joe61]

Here are the Circuit from that book, you got it wrong, the MOSFET is at the front not the back of the circuit.

You lost me there. By "at the front" you mean next to the battery connection? That's where it is in mine. I just have the battery connection on the right rather than the left like he does.

I did put a capacitor between before it. Is that what you mean?

Thanks

Joe

[billhowl]

But on the right is the 7805 output, you can't connect the battery to the output of 7805.

[joe61]

But on the right is the 7805 output, you can't connect the battery to the output of 7805.

Doh!

I was laying it out the way I wanted it to look on the board and completely missed that.

Thanks

Joe

(maybe I should stay with software ...)

[Soeren]

Hi,

I'm looking for a final size of 5 x 3 inches. I assume that the PCB will make the existing stuff more compact, so I was going to use whatever's left for the prototyping area.

I made it 4x3 (Eagle freeware max size).
Take a look at it and tell me what you need changed (like eg. the footprint of certain components or rearranging parts).

Instead of the MOSFET, I made a another polarity reversal protection with a fuse (which you should have anyway) and a diode - cheaper and with a still lower voltage drop.

Here's the circuit

Man I'm starting to feel really ignorant :-(

That's the first stage in learning 

[joe61]

I made it 4x3 (Eagle freeware max size).
Take a look at it and tell me what you need changed (like eg. the footprint of certain components or rearranging parts).

Instead of the MOSFET, I made a another polarity reversal protection with a fuse (which you should have anyway) and a diode - cheaper and with a still lower voltage drop.
Here's the circuit

Wow, thanks. I didn't mean for you to have to do the whole thing. That was really nice of you.

I'll study this and maybe have more intelligent questions later.

Thanks again

Joe

[joe61]

Here's the circuit

I'm finally getting some time to work on this and I have a question about the diode. I setup components on a breadboard according to the schematic, to make sure I understand it. The diode in the schematic is connected from Vcc to GND, but when I plugged in the battery I started smelling burning diode almost immediately. Seems like the diode should go in series, or did I do something wrong setting it up?

After a recent experience with a now-useless breadboard I'd like to be sure I know what I'm doing.

Thanks

Joe

[billhowl]

Did you connect the fuse? the diode connected in reverse direction to GND.
If current flow thought diode then you have connected battery in reverse.

[rbtying]

The point of the diode is to provide a least-resistance path through the fuse if the battery is connected backwards, and to provide essentially an open circuit if the battery is connected forwards. 

The arrow on the diode symbol (->|-) points in the direction of forward bias - you've got it backwards on your breadboard, if what you're saying is true.

[Soeren]

Hi,

The diode in the schematic is connected from Vcc to GND, but when I plugged in the battery I started smelling burning diode almost immediately. Seems like the diode should go in series, or did I do something wrong setting it up?

After a recent experience with a now-useless breadboard I'd like to be sure I know what I'm doing.

As others have already mentioned, either you mounted the diode backwards or you connected the battery backwards.

You cannot just leave out some components and expect it to work as designed for, you need the fuse (all circuits do really).

With the diode and the battery connected correctly, the diode will have no influence at all, as the diode is blocking the current.

If the battery is connected backwards, the diode will conduct the maximum current the supply can deliver for a very short while (and keeping the reverse voltage to the rest of the circuit down to one diode drop, which could be anything up to a bit over 1V, depending on what that specific diode drops at the current involved). Then the fuse blows. Without the fuse, the diode would melt down very quickly and short circuit your supply (battery).

Whether it was the diode or the battery that got in backwards, there's nothing else in the line of fire, so if the rest of the circuit burned, you must have other mounting errors.
Using the PCB would help getting it right (but cannot help with backwards installed components of course).

[joe61]

Hi,

The diode in the schematic is connected from Vcc to GND, but when I plugged in the battery I started smelling burning diode almost immediately. Seems like the diode should go in series, or did I do something wrong setting it up?

After a recent experience with a now-useless breadboard I'd like to be sure I know what I'm doing.

As others have already mentioned, either you mounted the diode backwards or you connected the battery backwards.

You cannot just leave out some components and expect it to work as designed for, you need the fuse (all circuits do really).

I didn't leave anything out, I set up the breadboard according to the schematic.

With the diode and the battery connected correctly, the diode will have no influence at all, as the diode is blocking the current.

If the battery is connected backwards, the diode will conduct the maximum current the supply can deliver for a very short while (and keeping the reverse voltage to the rest of the circuit down to one diode drop, which could be anything up to a bit over 1V, depending on what that specific diode drops at the current involved). Then the fuse blows. Without the fuse, the diode would melt down very quickly and short circuit your supply (battery).

Whether it was the diode or the battery that got in backwards, there's nothing else in the line of fire, so if the rest of the circuit burned, you must have other mounting errors.

The rest of the circuit didn't burn. I think your talking about my comment regarding another breadboard. I'm sure I did get something wrong. Sorry for the dumb question.

Thanks

Joe

[joe61]

Søren,

Sorry for my last response, guess I got a little defensive because I'm a bit frustrated over my lack of knowledge. I appreciate your help. I'll just work through it again on my own until I know enough to participate reasonably here.

Joe

[Soeren]

Hi,

Sorry for my last response, guess I got a little defensive because I'm a bit frustrated over my lack of knowledge. I appreciate your help. I'll just work through it again on my own until I know enough to participate reasonably here.

Nothing to be sorry for (and I didn't see your post as defensive at all).
Re-reading your former post, I can see that it wasn't this particular board that burnt - my bad for not reading it correctly in the first place.

A good way to go would be, to first build the power supply and just add a socket for the controller - then you can give it a smoke test and when it gives up no more smoke, start probing with a voltmeter, to check that it has the correct voltages at the relevant pins.

When you have that in place, turn off power, wait a couple of minutes to let the caps discharge and install the controller.

One good thing about CAD programs is, that the connections on the schematic gets to the board correctly. This is not always the case when using matrix board (and we've all been there at one time or another - He who never fail... Does nothing at all).