Feedback on schematic please...

Jed

I'm mainly concerned with the power, regulator, and the 8 connections to the stamp besides the I/O pins. Can anyone see anything that may spell disaster here or any recommendations before I solder everything? This is the first time I've taken a stamp off the development board and made my own stand alone so any feedback will definitely help me sleep tonight. sorry if the schematic isn't professional, I did my best.

UPDATE:
Ok, I updated the schematic attached to this post with the changes made. Everything look legit? I've scoured through a lot of posts and there are some contradictions such as whether to leave the programming & I/O pins floating or pull them up/down. I've decided to leave to diode on the regulator off since that's not on the BOE schematics and it'd just be more parts for me to solder. My concerns now are:

• Voltage Regulator, wired correctly with the caps?
• Power from regulator is going to the stamps Vdd pin and the stamps Vin pin is left floating. Is that ok?
• The cap next to the stamps Vdd pin, wired correctly?
• The 4 programming pins left floating.
• Pin 8 left floating (Will be set to output low in program)

Post Edited (Jed) : 3/1/2008 1:22:20 AM GMT

RDL2004

If that's a 3 terminal regulator in the upper left then it won't work. It needs to be like this:



A small (0.1 to 1uf) cap across the input (and output) would be a good idea also.

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- Rick

Post Edited (RDL2004) : 2/22/2008 2:33:04 AM GMT

Jed

What about pin 8? It won't be connected to anything. Can I just connect it to Vss? Do I need a resistor? And the other 4 pins (programming pins) can those float or do I need to connect those to something as well? Also, I see on the BOE rev C schematic that there's a cap on the reset button, but on the carrier boards' there is not. What's the reason for the cap on the BOE's reset?

RDL2004

I could be wrong, but I think the second·1000uf cap is actually on the output of the Stamp's on-board regulator, in case you use it to power other circuitry. You may not need it.

I've never bothered to put pullups/pulldowns on any unused pins on the Stamp and have never had any issues. YMMV, as they say.

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- Rick

Ugha

The second cap is on the on-board regulator from what I can tell.
If your going to use servos, I'd put the second cap on.

And don't use pullups/pulldowns on the programming pins... I was in the process of doing that when Chris Savage saved
my butt by telling me not to.

Check out my thread, it's pretty much identical to your problems.
http://forums.parallax.com/forums/default.aspx?f=5&m=251121

Chris Savage

RDL2004,

I would recommend the 1000uF capacitor to be on the regulator output…In fact, depending on the regulator there will usually be a specified capacitance required on the output. Usually more is fine and sometimes better. The input usually only requires a .1uF for noise. Both capacitors will usually help eliminate oscillation internal to the regulator.

The second capacitor is connected to the output of the BS2 on-board regulator and is there in case the Servos cause power supply dips that would otherwise brownout the BASIC Stamp.

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Chris Savage
Parallax Tech Support

Jed

Ok, the 2nd cap is on the stamp's Vdd pin... I thought it had something to do with the reset button. So, if I'm driving my servos off of the external regulator I probably don't need that.

Chris Savage

Correct…if your servos use a different supply then no, you don’t need that capacitor.

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Chris Savage
Parallax Tech Support

RDL2004

In the schematic attached to the first post, the cap on the regulator was configured as a DC blocking cap. That wasn't going to work too well [noparse]:)[/noparse]

I re-drew it as an input filter because I assumed a typical (poorly filtered, if at all) AC adapter would be what was used at the input jack. I can see how it would help to have another one on the output if there are servos downstream.

100uf per amp is the usual (rule of thumb) recommended size for the output cap, 1000uf per amp for the input filter.

edit: This is for the electrolytics, it is also usually recommended to have a 0.1 to 1uf on both the input and output, mounted as close as possible to the regulator.

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- Rick

Post Edited (RDL2004) : 2/22/2008 6:55:19 PM GMT

Ugha

What about another 0.1uf close to the BS2 and each IC? Is that needed or will the one close to the regulator be
enough?

So what your saying is...

input->1000uF->0.1uF->Regulator->0.1uF->1000uF->Project?

Configured as a filter of course, not in series [noparse]:)[/noparse]

Jed

So by removing the CAP on the stamp's Vdd pin, I basically need to just leave that pin floating and connect the RES pin to ground through a pushbutton. No resistors.

Ugha

I can be completely wrong and Vdd could be output only... but I think that if you have an external regulator you can run
the +5v into the Vdd and leave Vin completely unused. This'll bypass the BS2's onboard regulator and prevent voltage
drop from it as well as extending its life... I think.

At least that's what I THINK the super carrier board does, and what I had in my schematic... no one has said anything
about it so far so maybe that's right.

I'd wait and see if anyone replies to this before you try it though... I'm a bigger newbie than you are.

skylight

Jed I'd just like to say that I think it's a very professional job you did on the schematic, I'd be proud to produce results like that.

RDL2004

Ugha, your diagram is correct.

One other thing that's a "good idea" is a bypass diode across the regulator to shunt current past it when the power is shut off with·large capacitance on the output, like D1 in this diagram:





Here is a pretty good introduction to voltage regulators from National Semiconductor:

http://www.national.com/appinfo/power/files/f4.pdf

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- Rick

Post Edited (RDL2004) : 2/22/2008 8:51:02 PM GMT

Jed

Updated original post and schematic with changes. Input please.

Post Edited (Jed) : 3/1/2008 12:00:50 AM GMT

Ugha

As you know, I'm a bigger newbie than you... so be warned that my advice could be totally wrong.

Here's what I might have done different:
I'd tie the two VSS pins together.
I'd use the bypass diode that RDL2004 mentioned above.
Make sure you set pin 8 to LOW near the start of your program... if you do that, it won't be floating.
I'd also use the input->1000uF->0.1uF->Regulator->0.1uF->1000uF->Project setup that was mentioned
earlier.

Again, I'm a newbie and only half understand these concepts... so don't take my advice alone... use
it as a starting point to ask questions. (Also, any corrections on my ideas are welcome since I'll
be attempting something like this eventually).

Jed

I'm going to skip the diode, but thanks for the suggestion. I added the other caps, also as filters correct? And I already have PIN 8 set to output low.