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1  Using Arduino / General Electronics / Re: Voltage Regulators (LM7805) & Capacitors on: April 23, 2011, 06:27:54 pm
Thanks again to all the replies!

Based on the feedback here, I think I will not be adding the 7812 to the circuit.

But for clarification, the electric strike is a 12vdc 450mA from Kawamall. 

The schematics on the Instructable tutorial call for a leading 100uF/25v cap on the input of the 7805 and a following 10uF/10v cap on the output of the 7805. 

In my circuit, I've got a Fairchild LM7805.  The "typical use" schematic provided in the datasheet recommends a 0.33uF leading Cap and 0.1uF following Cap. The author of the Instructable didn't mention what manufacturer his 7805 was, so I looked at several online and couldn't find any that recommended a 100uF / 10uF combination. 

For the "ready state" of the circuit, it is pulling around 60-75mA waiting for an RFID card to be read.  When one is found to be correct, the current spikes to ~500mA total while the electric strike is activated.  Given these circumstances, how might one "guess" that the appropriate capacitor size needed for the 7805 should be the 100uF/10uF used in the current design when only 0.33uF/0.1uF is recommended in the datasheet? 

Based on everyone's feedback, I'm guessing that the Caps really wouldn't make-or-break the circuit at all in this scenario since most have suggested 'trial and error'.  Would it be a safe assumption to always opt for larger than necessary caps?  (without going overboard of course)

2  Using Arduino / General Electronics / Re: Voltage Regulators (LM7805) & Capacitors on: April 23, 2011, 11:54:31 am
Thank you both for your replies!  I will try to be more specific in my questions but I am not beyond doing a little homework, so if you have any specific questions about the hardware I'm dealing with please ask!

With the circuit from the instructables site set up on my breadboard I was able to see that at peak current the circuit was drawing just under half an amp.

Now, judging from the data sheets on the v-regs noticeably smaller selections of smoothing capacitors, I presumed that this was the "default" for the LM7812 under a constant load and at the minimum voltage required to keep the current flowing through the regulator. 

What I don't understand is the relationship between the "default" capacitors in the data sheet with those selected by the original author of the schematics for RFID door lock circuit.  I realize the reason for the larger capacitors has to do with the load placed on the regulator at certain points in time, but it doesn't appear to be a linear relationship (load doubles leads to capacitor size doubled)

What got me thinking about this was the fact that the original schematic doesn't have a 7812 v-reg in circuit... Only a 7805 for the arduino portion of the circuit.  So if I wanted to add that missing 7812, I would need to figure out / calculate the correct smoothing capacitors to the circuit along with the new 7812.

Again, thank you for your response... It is truly appreciated!
3  Using Arduino / General Electronics / Voltage Regulators (LM7805) & Capacitors on: April 23, 2011, 12:09:29 am
Greetings all --

I've spent the last several hours researching something I don't understand but have failed to figure it out on my own -- so I thought I would ask the experts smiley

I've been tinkering with a RFID Door Lock project I found at -- but I absolutely do not understand how the values for the capacitors on either side of the voltage regulator in the schematics were selected. 

I've looked at datasheets for both Fairchild and National for the 78XX v-reg's but found that the size of capacitors used in their examples were much smaller than those used in the schematic for the project I've been looking at.

The forums I have sifted through have provided some crazy-intense explanations of how to calculate for the size of a capacitor used with a v-reg, but I'm hoping someone can spell it all out in a much clearer fashion so I can grasp the concepts moving forward.

While I'm on the subject though, ... in the example project I noted above, the author is using a 12vdc Electric Strike Plate for the door lock mechanism.  According to his schematic, he's feeding 15vdc to the electric strike and then to the 7805 v-reg to supply power to the arduino.  Why would you not ALSO throw in a 7812 v-reg before supplying power to the lock mechanism?  And if you were to do so... it begs the question... what size capacitor would you use on the input side of the 7812?

Thanks for your help! smiley
4  Forum 2005-2010 (read only) / Troubleshooting / Re: AVRdude error -searched for hours, no solution yet on: April 02, 2010, 08:34:14 pm
Royal newbie error.

I'm deeply shamed to report that I've found the solution to my problem.  And thanks to the suggestion by mawe, no less.

I discovered that nothing was flowing on my TX / RX lines.  This confused me a great deal because I double and triple checked everything to ensure it was spec'd, placed, and connected appropriately.  

Or so I thought.

After a great deal of frustration and angst, I decided it was time for a cigarette.  It was during THIS time that it hit me.

"I wonder if the TX/RX lines on the USB-TTL board are NOT in fact the true TX/RX lines as they relate to the ATmega chip."

A simple swap of my connections... TX on USB-TTL to RX on ATmega328p and BAM... fixed.

What a great sense of accomplishment... however small it may be!

Thanks again mawe!!
5  Forum 2005-2010 (read only) / Troubleshooting / Re: AVRdude error -searched for hours, no solution yet on: April 02, 2010, 05:48:35 pm
I have tried changing ports, but I'm fairly certain I'm supposed to be using COM 4 for my machine.  Without the USB plugged in, COM 4 disappears, and my system device manager indicates that COM 1 is a printer port (only COM1 and COM 4 available in Arduino software environment)

The board I have selected is "Duemilanove or Nano w/ ATmega328"

And zero wireless devices are connected to my PC.
6  Forum 2005-2010 (read only) / Troubleshooting / (SOLVED) AVRdude error on: April 02, 2010, 05:05:23 pm

I put together an Arduino on a breadboard using a tutorial I found at

You can view a photo of my build using this link:

The only variance from the tutorial I followed was that I used a USB-BUB from Modern Device... and I connected an LED to the 5v power as a visual indicator that the board was getting power.

When I attempt to program from the Arduino software environment, I get the following error:
avrdude: stk500_getsync(): not in sync: resp=0x00
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

I've been searching the forum, Google, and the Arduino Troubleshooting page for the last couple of hours but I can't seem to identify my problem.

One question DOES stand out to me, however... how long should I depress the RESET button... and at exactly what TIME in relation to clicking the UPLOAD button in the Arduino software?  I suspect that this may be part of my problem.

I did a couple of tests... but unfortunately they told ME nothing -- they might tell you fellows something though.  I have two batches of ATmega328p chips... one set I purchased virgin and burned the bootloader myself with an AVR Dragon board... the other set I purchased from SparkFun with the Arduino Bootloader pre-burned.

Switching between the two yielded an interesting difference.  While I get the SAME error when trying to upload a new sketch, the LED on pin 13 behaves differently.  

With my self-burned bootloader chips, the LED flashes very briefly followed by a 2 second (or so) pause and then repeats.  When I press the reset button, the blinking continues again virtually immediately (no noticable delay).  Pressing and holding the reset button stops the LED from flashing as long as it is depressed.

With my pre-burned bootloader chips, the LED flashes rapidly, getting faster and faster until it reaches peak brightness then it goes out.  This happens within 3 seconds.  When I press the reset button, the process repeats and the LED is dark again within 3 seconds or so.

So this raises another question... with a fresh chip, what SHOULD the behavior on Pin 13 be?  Flashing?  Dark?

Any help you could provide is truly appreciated.  I'm getting frustrated with this setup.  I've stripped the breadboard down and started fresh twice since the first build, but I keep getting the same results.

Thanks again!

[edit]One last thought... is there a way I can change my curcuit to have the Arduino auto-reset when attempting to upload a sketch? Perhaps that'd help with some of the problems!!![/edit]
7  Forum 2005-2010 (read only) / Troubleshooting / Re: found schem for simple avr prog but have some Q's! on: March 11, 2010, 12:04:56 am
All the more convenient!   smiley-sad
8  Forum 2005-2010 (read only) / Troubleshooting / Re: found schem for simple avr prog but have some Q's! on: March 10, 2010, 08:16:35 pm
Ok... another thought.  Can anyone confirm that the dsub 25 pins referenced in the schematic at are even correct?  

I found another schematic at with an entirely different parallel pin configuration.

9  Forum 2005-2010 (read only) / Troubleshooting / Re: found schem for simple avr prog but have some Q's! on: March 10, 2010, 07:58:32 pm
One other thought...

Should I be using PonyProg or just stick with the Arduino software...?  I've tried both.
10  Forum 2005-2010 (read only) / Troubleshooting / Re: found schem for simple avr prog but have some Q's! on: March 10, 2010, 07:54:41 pm
As far as I can tell, everything is connected according to the schematic I found.  

Here are a couple of shots of the board as it sits...

The VCC and GND pins are connected.  I'm not familiar with a "bypass capacitor" ... (I'm completely and utterly new to this aspect of electronics, but I'm learning!)

I am using the most recent version of PonyProg (2.07c).

Concerning the length of the wires / cable to the AVR, I'm not entirely sure what you mean.  I've got a 6 foot parallel ext cord from my PC coming to the cable I've soldered.  I was very careful when soldering to ensure no accidental bridges.

16MHz - FOX160 crystal... two 22pf caps in front of it.
Voltage Reg is 7805 12v
The rest of the parts list can be found at

I'm powering the board with a 9v battery.

The little labels on the wires at the top of the board represent the leads from my d sub connector...
TOP wire is MISO
THIRD wire is MOSI
FOURTH wire is SCK

The chip is an atmega328p.

I'm running PonyProg is WinXP and installed GIVEIO and modified the system registry to set "DisableWarmPoll"=dword:00000001

Please ask whatever questions you think of and I'll do my best to provide answers as promptly as possible.  Just remember that I am very new to this and often find myself resorting to googling acronyms I (frequently) don't understand.  As I said in an earlier post, I'm one of those people that finds it easiest to learn to swim by jumping in the deep end of the pool...  

I absolutely appreciate your time and feedback!

11  Forum 2005-2010 (read only) / Troubleshooting / Re: found schem for simple avr prog but have some Q's! on: March 09, 2010, 09:08:27 pm
Thanks so much for the fast reply! I'll certainly take your advice into consideration... But I'd like to continue tinkering with my parallel schematic for a while.

While I'm looking forward to getting my first Arduino up and running, part of my journey (and my ultimate goal) is learning both the HOW and the WHY... Building a unit from utterly nothing would be a tremendous amount of pride ... So while I may ultimately have to give up on it (even if only temporarily to buy a tried-and-true programmer) I still want to figure this bad boy out!!  
12  Forum 2005-2010 (read only) / Troubleshooting / found schem for simple avr prog but have some Q's! on: March 09, 2010, 08:44:01 pm

I've been feverishly finding parts to get started with building my first Arduino, but naturally I've run into a few snags and am HOPING someone can help shed some light.

FIRSTLY -- I'm attempting to build my own Arduino from scratch.  I've acquired all the parts (I believe) including a few atmega328 chips (not preloaded with bootloader).  Why, well... because I suppose I like doing things the difficult way!! (helps you learn faster, IMO!)

So first things first... I have to get the bootloader onto the chip!  I found some spec's to build a seemingly simple AVR programmer online (see note below!!) which I built... but with absolutely zero success.  

I'm hoping someone with much more experience than I can tell me if this would even work... or if I'm just running in circles.

The forum won't allow me to post a link in this post because it is my first time using this forum, HOWEVER, if you google "make your own ultra simple universal avr programmer" it should be the first link Google returns.  

Thanks a bunch!!
13  Forum 2005-2010 (read only) / Development / seeking guidance/advice using AVR Dragon on: April 02, 2010, 09:15:01 pm
I'm looking for guidance / advice / wisdom from all folks out there that have experience using AVR Dragon from Atmel.

I just got mine yesterday and I've played around with it all day today but I fear I've managed to brick several ATmega chips with it.  It seems almost too easy to be able to make a chip unusable!

So if you have any input or even if you could direct me to some helpful websites with valuable information / instruction / tutorials dealing with the AVR Dragon I would be extremely grateful.

Some general questions for those with experience...

1) How realistic is it that I've bricked a few chips with the ISP interface of the AVR Dragon even though I didn't necessarily start a write process?

2) Can seemingly "bricked" chips be saved via PP/HVSP programming? If so, how?

3) Why do pre-burned-bootloader chips from SparkFun not read properly and cause problems when I try to simply "Read Signature" on them in my AVR Dragon?  It seems to give me the same response as the chips I fear I've bricked already!  "Entering programming mode... FAILED"

Again, any tidbit of knowledge you can offer is very valuable here!

Thanks for your help!
14  Forum 2005-2010 (read only) / Development / Re: 3.3v vs. 5v and programming via usb on breadboard on: March 26, 2010, 10:00:11 pm
I decided to give the BUB a try and it should be here this next week. Since I'm so new to this, don't be shocked if I come back to the boards for another slice of your wisdom!

Thanks to all that have commented. Again, the folks here on the Arduino forums have been tremendously helpful. It's so nice to be able to find a new hobby that has as supportive of a community as this.

Any tips/suggestions for when my new BUB arrives?
15  Forum 2005-2010 (read only) / Development / Re: 3.3v vs. 5v and programming via usb on breadboard on: March 25, 2010, 11:21:58 pm
Again, I have to apologize for the lack of understanding on my part, but... The USB-BUB...I see that it would require me to solder headers to the board, which is fine I have no problems with that, but how would I connect it to the circuit to program / power my breadboard arduino? Is it as simple as using jumper wire or would it require something like a special cable or other hardware?

Thanks so very much for your time in replying! These forums have been a true WEALTH of information!!!
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