Go Down

Topic: Data over power ... (Read 2 times) previous topic - next topic

pwillard

With this thread, I am reminded of how impressed I was with the Lego Mindstorms 1.0 sensor/controller bus solution...

polymorph

I would think with a schottky diode, you'd be fine as it would be less than the voltage required to forward bias the internal protection diodes. However, it is as simple as adding a diode in series with the line going to the receiving Arduino to drop out one diode drop of voltage.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

jack wp

#17
Aug 07, 2013, 08:32 pm Last Edit: Aug 07, 2013, 08:35 pm by jackwp Reason: 1
Is this pretty close?
Schematic attached.

I attached a .jpg file, but can't see in in preview. I will post to see if it is really there, if not, I will remove this post.

UPDATE: the jpg did attach, but when clicked it is really to large. Is there a way to adjust that image size? Sorry if off topic.
Good luck, Jack

majenko


UPDATE: the jpg did attach, but when clicked it is really to large. Is there a way to adjust that image size? Sorry if off topic.

Yes, it's call gimp (or photoshop for those lah-di-dah enough to pay for software ;) )
Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

polymorph

What are you making the schematics in? When you export, is there an option for adjusting the size?
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

jack wp

I just downloaded Fritzing, and this was one of my first 3 tries. I have not found a way to adjust the size.
In Fritzing, I used File - Export - As Image - Jpeg. I saw no options for adjusting the size. I am searching Fritzing for that option.
Good luck, Jack

Nick Gammon


UPDATE: the jpg did attach, but when clicked it is really to large. Is there a way to adjust that image size? Sorry if off topic.


Depending on your operating system, most image viewers have a resize option. The Gimp is free.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

Riva



UPDATE: the jpg did attach, but when clicked it is really to large. Is there a way to adjust that image size? Sorry if off topic.


Depending on your operating system, most image viewers have a resize option. The Gimp is free.

XnView is a nice little image viewer that can crop, resize etc and it's multi-platform now.
http://forum.arduino.cc/index.php?action=unread;boards=5,67,10,11,66,12,15,17,21,22,23,24,25,29;ALL

Nick Gammon


@Nick:

Here is one rather mature uC network:
http://www.kranenborg.org/ee/picaxe/twowirenetwork.htm


I'm trying to make this up, and have hit a snag. Either I am misreading the circuit, or mis-assembling it, or there is a typo in the circuit. This is it:



Does that look right? Or are the transistors around the wrong way (NPN/PNP)?

I swapped them (unless I have put them in wrongly in the first place) and the output looks much better.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

majenko

They look the right way to me... PNP on top (high side) and NPN on the bottom (low side).  It looks like a basic high current two stage push-pull output to me.
Get 10% off all 4D Systems TFT screens this month: use discount code MAJENKO10

Riva

Do you have the MOSFETs the right way round?
http://forum.arduino.cc/index.php?action=unread;boards=5,67,10,11,66,12,15,17,21,22,23,24,25,29;ALL

tmd3

Caveat:  FET's aren't really my area of expertise.  The superior man reaches his own conclusion.

From the datasheets, T3 turns on when VGS is below about -4V, and T4 turns on when VGS is above about 3V.

With the serial pin high, T1 is off and T2 is on.  T2 collector voltage is low.  VGS for T3 is -5V, and close to zero for T4.  T3 is on, and T4 is off.  Output is high.
With the serial pin low, T1 is on, T2 off.  T1 collector voltage is high.  VGS for T3 is close to zero, and 5V for T4.  T3 is off, and T4 is on.  Output is low.

The 4K7 resistor between the gates slows gate charging on the active FET, so that it turns on more slowly than the inactive FET, preventing them from both being on simultaneously.  It's likely that you'll see a short period when the output is open-circuited after the serial pin switches, and that may be why the output doesn't look as good as you'd hope.  With this circuit, turn-on time will certainly be limited by the 4K7 gate resistor, and that will limit the switching rate that you can use.   The datasheets suggest that the effect will be more pronounced when the output switches from low to high.  


jack wp

Well it does not really look right to me.
If the serial out was at, say 2.5 volts. That would cause both transistors to turn on wouldn't it?
Good luck, Jack

polymorph

No, on the contrary. With the serial out at 2.5V, both MOSFETs are -off- because both Bipolar transistors are -on-. The circuit is designed specifically so that both MOSFETs are never on at the same time. The upper P-MOSFET is only on when the Serial Out signal is at or near 5V, and the lower N-MOSFET is only on when that same signal is at or near 0V.

You could build it and try, or enter all that into a Spice simulation and see what you get, but I suspect the switching points are roughly above 4V and below 1V. Between that, both MOSFETs are off.
Steve Greenfield AE7HD
CET Consumer Electronics and Computer
Please don't read your attitudes into my messages

jack wp

Thanks polymorph for the clarification.
I know just enough to be dangerous, but I learn something new all the time.
Good luck, Jack

Go Up