What is the function of 68 ohm resistor connected between USB and PORTB in USBASP?

• Jul 19, 2010

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mehta.vishal.360

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I am new to AVR so hope u dont mind my stupid question in the circuit of usbasp can any1 explain me wht is the use of 68 ohm resistor(other thn current limiting) which is connected between USB and PORTB of atmega 8 can i use any other resistor???

 

• Jul 19, 2010

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sidy50

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USBASP for avr....

Friend, refer to this topic . It contains all the information u need...I have built 1 USbasp & have uploaded the modified & Perfectly Working schematics & layout using Target PCBpool...Even i have changed some resistor values...Download the file...Itll help u...Regards

 

• Jul 19, 2010

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Re: USBASP for avr....

thx a lot i will be completing the circuit by tmrw thnks once again

 

• Jul 19, 2010

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sidy50

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USBASP for avr....

Do let us know about the results...Regards

 

• Jul 19, 2010

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Re: USBASP for avr....

sidy thx a lot for help but i am unable to open the files cause i dont have target pcb can u just send me the circuit diagram like given in 8051projects site.....if its possible for u....thx once again

 

• Jul 19, 2010

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sidy50

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USBASP for avr....

Vishal m very sorry...I dont have access to PC right now, m browsing through my smartphone...But u can open those files...Google for "Download Target PCBpool dicovere"...and download it...u can open them using this software also it is good PCB designing software...Hope it helps...

Regards.
sidy.

 

• Jul 20, 2010

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Re: USBASP for avr....

Sidy i did test he circuit today it showed "windows cant recognize the device" i did install the usbasp driver from net but still it showd tht.....need help ......i have made the circuit according this site https://www.fischl.de/usbasp/

 

• Jul 20, 2010

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pranam77

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Re: USBASP for avr....

mehta.vishal.360 said:

Sidy i did test he circuit today it showed "windows cant recognize the device" i did install the usbasp driver from net but still it showd tht.....need help ......i have made the circuit according this site https://www.fischl.de/usbasp/

Click to expand...

You didnt mention that wether you have constructed the circuit o a PCB or on a vero board. There are quite a lot chances of swapping the USB communication Pins when the circuit is assembled on a veroboard. Cross check the same which is a common mistake. Also confirm that you have programmed the correct fuses on the firmware chip as per the article.
Cheers

 

• Jul 20, 2010

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Re: USBASP for avr....

I guess the thing is tht i think so atmerga 8 wasnt programmed properly...i m makin serial programmer again in order to program atmega 8 first....any comments???

Added after 1 minutes:

And yes i have made the circuit on a PCB....

 

• Jul 20, 2010

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sidy50

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USBASP for avr....

Did u program the Fuse Bytes?

Added after 1 minutes:

Did u program the Fuse Bytes of Atmega8 while programming it?
It is very important...without that it wont function...

 

• Jul 20, 2010

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Re: USBASP for avr....

i havnt properly programmed the amega8 i am right now makin pony prog circuit to program it....

 

• Jul 20, 2010

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sidy50

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USBASP for avr....

Vishal refer to this topic, before programming the Atmega8 u have to set its fuse bytes, load the hex file & then program the IC.This post has a pic displaying the fuse bytes then after that pranam made a post, telling the exact Fuse Bytes to be programmed..

 

• Jul 20, 2010

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Re: USBASP for avr....

thx a lo...i will do tht....

 

• Jul 23, 2010

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Re: USBASP for avr....

sidy am programming atmega8 using avrispmk2 as i dont have a serial port...tht means i need to vary the circuit given by fischl according to avrisp rite???

 

• Jul 23, 2010

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sidy50

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USBASP for avr....

Buddy ur programming circuit has nothing to do with the Fischl's circuits...Whther u program the Atmega8 by USB programmer or any other programmer just take care, u program properly with appropriate fuse bytes...u cannot program the atmega8 when it is in the Fischls circuit...program it separetely on a breadboard or the way u find convienient...then put the programmed Atmega8 in the main circuit (Fischls circuit) & now when u connect the USBasp to Pc ...it would ask for driver...

 

• Jul 23, 2010

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Re: USBASP for avr....

thx buddy i did program atmega8 using avrstudio and so i had to just check the crystal oscillator thing......my usbasp is workin nicely....

 

• Jul 23, 2010

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sidy50

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USBASP for avr....

Awesome man...nice work...Cheers.