Show Posts
Pages: 1 2 [3] 4
31  Forum 2005-2010 (read only) / Development / Re: Questions about making a custom Arduino board on: August 21, 2010, 08:12:17 pm
Ok so I've solved most of the problems the only real good question I can think of right now is. I have left the ICSP headers off of the schematic cause I feel they take up alot of room. Is there a way, or could someone explain to me how I could load the bootloader onto the atmega1280 without have to use the icsp headers. I've been doing some research on it but im just confused.

Thanks again guys :-)
32  Forum 2005-2010 (read only) / Development / Re: Questions about making a custom Arduino board on: August 17, 2010, 11:22:04 am
Thanks for the quick reply. Few more questions while im at work :-) I will review everything tonight.


Quote
For enabling / disabling the auto reset circuit when you cut the trck to disable it.

What is the default on the arduino mega board? Enabled?


Quote
To the reset pin (pin 1)?

So if I was to pull the reset pin out of the schematic... Would the button still work? <- More research on my end is needed

Quote
Vin is the input voltage before the regulator. It is connected to the comparator to automatically switch the supply from USB to external power when an external power source is supplied.

Same as the reset pin question, if I remove the pin that goes to the header on the regular arduino will it interfere with its operation. Cause i notice the schematic shows it running towards the vin but I can't see why it just goes to the VIN pin header. (Maybe im just very confused.)

Ill check out that link tonight, thanks for not flameing my n00bishness.
33  Forum 2005-2010 (read only) / Development / Questions about making a custom Arduino board on: August 16, 2010, 10:05:16 pm
So Im trying to go about condensing the arduino schematic for my project. But i've run into a few problems that I can't find a clear answer for. Hopefully someone on here could lend a hand.

1)  First off when going through the USB portion of the schematic I came across the Vin part of the board. Do I need it, cause it seems like its just for a header. And if I were to remove it how far back do I go in the circuit.

2) Also for the reset button in the bottom left corner of the schematic where does it go to, I see the USB and the capacitor / +5V in the top right using it where could I move the reset button too to get rid of the bottom right circuit?

3) The Solder Joint 1 (SJ1) in the USB circuit, what is it used for?

4) I don't want the standard power plug. Perferably just powered from a lithium battery, with the small two prong connector.
Any good links on incorporating that into the design?

eg. http://www.sparkfun.com/commerce/product_info.php?products_id=8483


5) Will I be able to load the boot-loader through the USB the way this schematic is set up? (Without the ICSP jumpers)

Thanks a bunch. Geoff :-)

And finally the Schematic

34  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 08, 2010, 09:16:16 pm
Haha, I just can't win. I forgot the voltages will be to low to read HIGH and LOW now :-/ It will only return a low value.

Whats my best option? Op-amp or something?

Geoff
35  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 08, 2010, 11:45:38 am
Its not actually publicly available. It does actually come with a disclaimer, the code I'm provided with I can't distribute at all. I'm allowed to show my code though. I think its to limit and control who has the information.
 
The mix up was on there end with two identical parts but three revisions of the same ic and still providing the different versions for backward compatability.

Geoff
36  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 08, 2010, 10:56:16 am
I really appreciate your help, normally when I'm having troubles I will post a datsheet, in this specific case though I don't have permission to post in a public forum. By all means I can send an email with the disclosure statement, but not in public.

I have talked to a few people about it and a couple engineers and I'm hoping this is why the chip isn't operating. Origonally I was sent two different datasheets for chips with the same identification codes. But it was a mistake on there end and they are fixing it. Now that I have the correct sheet I'm starting to see some differences especially the current consumptions and the inputs are all different.

Again thanks for all your time, and once finished, the project will be publicly available.

Geoff
37  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 07, 2010, 06:37:00 pm
Ok so far this is what I have let me know if im shooting in the dark lol.

1A)So that means if im using the level shifter I have, I won't be able to detect the LOW output from the ASIC?

1B) If thats true then I should just use some resistors for now to breaboard.

I/O Pin 6(5V) <-> 1.8K Resistor <-> ASIC <-> 3.3k <-> GND      //DATA
I/O Pin 7(5V) <-> 1.8K Resistor <-> ASIC <-> 3.3k <-> GND      //STROBE


Quote
3) The LVC MUST be powered from 3v3 in order for this to work.
2) How do you mean. I have it powered from 3V3 but it changes the 5V from the arduino I/O pin to 3V3 for the ASIC

*I should also mention the 5V I was talking about was the I/O pin supply voltage its 5V, 40-5mA i believe.
38  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 07, 2010, 06:05:16 pm
Ok, so on the data sheet the STROBE on the ASIC is just used to take inputs from the arduino for setting it to HIGH or LOW.

for strobe it says "STROBE Protection Diode Current" 20mA

and the DATA line is used to pull information from, when it goes LOW
but initially I have to set it to HIGH.

My problem is that its maximum voltage is 3.6V.

And maybe im still all confused, but if I use the level converter it will drop it to 3.3V which is within its voltage requirements and current?.

so as i think your saying

ARDUINO  MEGA

I/O Pin 6 <-> (5V) LVC (3.3V) <-> resistor -> ASIC       //DATA
I/O Pin 7 <-> (5V) LVC (3.3V) <-> resistor -> ASIC       //STROBE

Could you explain what he mean by

"the ASIC can only guarantee 0.4V when sinking up to 2mA. "

I've been working on interfacing for a while now, and the only thing i can figure is the problem is this part with the sinking which im not understanding.


edit: added to
39  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 07, 2010, 03:46:42 pm
Actually I should mention since I still havn't got this chip running, I think I might of fried it.

So in the datasheet it also mentions that there is a DATA and STROBE protection DIODE for sinking, max is 20mA and min is -20mA

I emailed the company that provides it and they wrote me this,

"The DATA and STROBE line will NOT be able to sink 50mA. Even the 20mA is not recommended as this is absolute MAX. Our datasheet shows the ASIC can only guarantee 0.4V when sinking up to 2mA."

So going back through what you guys said, I should just use resistors in series to lower the operating voltage/Current of the I/O pin to an acceptable level.

Will I still be able to send digitalwrite(HIGH) or LOW Commands to the chip operating at this low of a current?

And I guess if this is the case 3.3V droped by that level converter did fry the diode. (silent but deadly) haha

Hope someone can get back to me. Much appreciated.

Thanks
Geoff
40  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 01, 2010, 07:50:01 pm
hahaha, yeah that one :-)

Its actually already bread boarded and working for an sd.

Thanks so much for all your guys' help
41  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 01, 2010, 07:41:04 pm
Ok so I can use that level shifter i posted earlier and everything will work out fine :-)

"I already have that level shifter in a box somewhere"
42  Forum 2005-2010 (read only) / Interfacing / Re: 5V signal down to 3.3V and only 20mA on: October 01, 2010, 07:15:06 pm
Ok, but won't that drop the voltage?

Ok so as an example if it needs 20mA max but and you connect directly to the arduino I/O pin its supplying 40mA. Won't it fry the chip. Im really confused on this, I understand it draws what it needs but when sending a signal that will be at 40mA right?
43  Forum 2005-2010 (read only) / Interfacing / 5V signal down to 3.3V and only 20mA on: October 01, 2010, 06:08:13 pm
Hello hope someone can shed some light on my situation.

I have a small ASIC that is powered from the 3.3V pin on the arduino mega.

The ASIC receives I/O on two digital lines, DATA and STROBE. I have it connected to pins 18 and 19.

My problem is that DATA and STROBE can only handle 20mA MAX and 3.3V the arduino mega on those pins sends out 5V and 40mA


I was thinking of using a sn74lvc245a to convert the levels down to 3.3 but that would supply to much current.

link to datasheet:
http://focus.ti.com/lit/ds/symlink/sn74lvc245a.pdf

The ASIC can handle -0.3 to 4.0 V

So I can use a variety of voltages but I need to limit current.

Anywho hope you guys/gals can help me out.
Cheers
Geoff
44  Forum 2005-2010 (read only) / Interfacing / Serial Commands without FTDI chip on: August 30, 2010, 06:23:37 pm
Just a quick question. Can I send serial commands from the rx, tx pins without the FTDI chip.

Im trying to setup a thermal printer to print off stored GPS coordinates from an onboard SD card. But I don't need it connected to a computer through its serial port, I just need it to receive from the atmega1280 chip.
45  Forum 2005-2010 (read only) / Interfacing / Re: Thermal Printer Mechanisms on: September 02, 2010, 10:56:47 pm
I appreciate your help. Ill do some more research and if I run into some more troubles ill post back :-)
Pages: 1 2 [3] 4