5V Output Question

djh82uk

Hey guys, I have just received my propeller proto board after long being a pic/picaxe user.

Im struggling a bit with getting into spin, but that is for another thread as and when I get stuck.

All Im trying to figure out right now is what is the best way to have a 5V ouput, basically I need to switch 5V on and off, it was never a problem with the picaxe as it ran at 5V anyway, I thought about a darlington driver but it seems they need a 5V input.

Could someone please advise along with a part number if possible?

I will be switching the 5 V between 5 different jumpers on the mainboard of another system.

I also need the info so I can apply it to powering 5V relays for which the darlington would have been great.

Regards

DJH

Martin Hebel

First, verify that you need a full 5V. 3.3V is above the threshhold for many 5V inputs - that is, it may well be sensed as a high even though not at a full 5V.

An transisitor can be used as a level shifter, the collector is pulled up with a resistor to 5V with the 3.3V to the base driving it. Note: depending on the configuration you use, it may be inverted - 3.3v on base give ~0V out, and 0V on base gives 5V out.

-Martin

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StampPlot - GUI and Plotting, and XBee Wireless Adapters
Southern Illinois University Carbondale, Electronic Systems Technologies

Anubisbot

Hi,
you can use a logic Mosfet for that, i use them to switch 12V.

the Digikey part numer is NDS355NCT-ND it is a SSOT 3 and is rated with 30V 1.7A

They work great.

Anubisbot

djh82uk

Thanks for the help guys, I tried it at 3.3v and it does not register [noparse]:([/noparse]

The problem with the mosfet is taking up board space on the proto board as I would need at leat 6 of them I guess.

Would a NPN transistor suffice on each line? Would they be switched ok at 3.3V?

Sorry, im terrible with the theory side of things [noparse]:([/noparse]

DJH

tekochip

If you have several lines that need voltage translation use an LVC07 buffer.· You will need a pull-up on the output because these parts only sink (pull low).

http://focus.ti.com/lit/an/scea012/scea012.pdf

Here's a better link, look at page 6

Post Edited (tekochip) : 6/8/2007 1:46:50 PM GMT

Martin Hebel

Just to verify the 3.3V won't work... you do have a common ground between the systems ?

-Martin

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StampPlot - GUI and Plotting, and XBee Wireless Adapters
Southern Illinois University Carbondale, Electronic Systems Technologies

djh82uk

Hiya

I tried it without any propeller, I just had it with a normal switch to change between jumpers, I tried putting resistors between them which knocked it down to 3.6v at which point it failed to notice the jumper was connected.

Regards

DJH

Martin Hebel

If the resistance was in series, you would have been approaching the input impedance of the input, which can be quite high. You don't say what resistance you used, but you may have reached a point there was insufficient current as opposed to an issue with the voltage.

It shouldn't damage anything if you simply just test using the output of the Propeller.

-Martin

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StampPlot - GUI and Plotting, and XBee Wireless Adapters
Southern Illinois University Carbondale, Electronic Systems Technologies

djh82uk

ok I feel stupid now,

I was using a 22k and a 220k in series

I will try the prop, just need to write some code for it, im still figuring out spin but am impressed so far (im used to basic)

whats the max voltage the proto board can as power supply? The main board has a 9V PSU but gives out 13v (unlucky? :P) tho I have 49 of them and they are all 12v-13V, guess I could look up the voltage regs for a data sheet.

Im still reading the manual, something else I was wondering, is it possible to store variables in the eeprom so that are retained after reboot?

The picaxe had a read and a write command where you could save a word variable.

Basically I want it to remember the state of the switch when just has to be 1 or 0 (twice as 2 switches).

Also another random question (same project), the mainboard I am using will be outputting to an RGB Scart cable, now does and RGB scart cable also have a composite pin? or can I split the signal into RGB like the vga out? Obviously vga out will be no good due to resolution/sync etc im assuming.

Thanks for all your help, it's very appreciated, as times goes by I will stop asking annoying questions,

DJH

Martin Hebel

It's ok, this might make up for all my stupid answers recently!

The protoboard will be fine on 12-13V

As to permanently storing data, the protoboard has a larger EEPROM than is required for the propeller code image. You can write/read the higher areas of EEPROM. Do a search for EEPROM I2C objects.

Not sure about your RGB question, sorry.

Keep the questions coming, but be sure to look through the forums or search them at search.parallax.com

-Martin


-Martin

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StampPlot - GUI and Plotting, and XBee Wireless Adapters
Southern Illinois University Carbondale, Electronic Systems Technologies

parts-man73

djh82uk said...
whats the max voltage the proto board can as power supply? The main board has a 9V PSU but gives out 13v (unlucky? :P) tho I have 49 of them and they are all 12v-13V, guess I could look up the voltage regs for a data sheet.

That's quite normal for a wall wart to show that high of a voltage with no load. Once you plug it into the protoboard, you'll see that drop to the rated voltage. Just be sure it's a positive center, I don't see any reverse voltage protection diodes in the schematic, I'm not sure what would happen if you plugged in a negative center power supply, but I don't want to be the first one to find out.

I have used the power supply for my laptop to power a protoboard once. It worked fine, but the 5 volt regulator get hot quickly. I believe that regulator is actually rated for a maximum input of 35volts, but the higher the input voltage, the more heat it must dissipate.

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Brian Meade

"They who dream by day are cognizant of many things which escape those who dream only by night" - Edgar Poe

djh82uk

Thanks for all the info [noparse]:)[/noparse]

will replay back once I have tested it, the psu powers the mainboard, I was going to spur off that to power the proto board, it does drop but only down to about 12V

Im having fun playing with it tho [noparse]:)[/noparse]

DJH

djh82uk

one other little question, im used to picaxes as I said before, so don't want to assume anything, Part of the circuit is a push to make switch between a pin and ground, do I need a resistor to limit the current or will it be ok?

DJH

Propability

Well I've accidently plugged a negative center wall-wart into the protoboard and when the power led failed to come on I turned it off immediately.Plugged a correct one into the board and all seems OK. I think there is a post here about the regulators used having a reverse voltage protection.

parts-man73 said...

djh82uk said...
whats the max voltage the proto board can as power supply? The main board has a 9V PSU but gives out 13v (unlucky? :P) tho I have 49 of them and they are all 12v-13V, guess I could look up the voltage regs for a data sheet.

That's quite normal for a wall wart to show that high of a voltage with no load. Once you plug it into the protoboard, you'll see that drop to the rated voltage. Just be sure it's a positive center, I don't see any reverse voltage protection diodes in the schematic, I'm not sure what would happen if you plugged in a negative center power supply, but I don't want to be the first one to find out.

I have used the power supply for my laptop to power a protoboard once. It worked fine, but the 5 volt regulator get hot quickly. I believe that regulator is actually rated for a maximum input of 35volts, but the higher the input voltage, the more heat it must dissipate.

Pete