ere ISPAVRU1 USB programmer question

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Hi :)
I have one of the new ere programmers..

I am building a board with the ISPAVRU1 and a zif socket.
My question is, can I tap the USB port to get the 5v that I
need to power the Atmel chip in the zif?
I have tested my new board by plugging an atmega168 into
the zif and powering the 168 using a seperate 5v supply..and
it works just great. I was about to change from the external
5v supply and tap the 5v from the same USB port that is powering
the ISPAVRU1 but I decided to ask for advice here first before
I make smoke come out of this thing :)

I'd sure hate to have to use an external 5v supply for the chip..
my hope is to use the USB to power the ISPAVRU1 and also
the chip that is to be programmed....do you guys think this will
work?

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Hi Gwen

I steal power from USB for my breadboard and it works just fine. I use a parallel port programmer though. I can't imagine it not working with a usb programmer.... standard disclaimers apply though.

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You can steal 500ma off the USB at 5V, or 100ma off a non-powered USB hub. The USB system has protection on it - ever seen a "the is not enough power on the USB bus, etc." messages in Winblows?

- Dean :twisted:

Make Atmel Studio better with my free extensions. Open source and feedback welcome!

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Hi guys :)

Yeah, I know I can get enough power from a USB port to power a
small circuit board or supply an AVR chip so that it can be programmed.

What I am concerned about is what might happen to the ISPAVRU1
if I connect the V+ and Gnd pads from the USB end of the programmer
to the V+ and Gnd pads on the 10-pin isp connector end of the ISPAVRU1?
I mean, might this cause some problems with the voltage regulation or
whatever for the ISPAVRU1? I worry that it might just go belly-up if I
do this...but i sure want to do this.

The V+ and Gnd of the ISPAVRU1 isp connector reads 4.5v ...but this does
not manage to pass enough current to actually power the AVR chip so that
it can be programmed.

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Here is a link to the PDF manual for this thing...maybe someone not
as clueless about electronics as I could look it over and make a judgement
re this. http://www.ere.co.th/download/is...

I just had a thought...do not all the USB ports on a PC have their V+ and Gnd
lines in common? and if so, then people who regularly use the 5v pwr from the
USB to power circuit boards with AVRs on them (like I do) and who also use
the ISPAVRU1 to program the same boards will in effect be connecting the
V+ and Gnd lines from one end of the ISPAVRU1 to the other.....hmmm
this is bound to happen so maybe the guys at ere thought of it and made sure
it is OK.

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Quote:
Where did you measure the 4.5V? Right on the PCB USB connector?

No, that measurement is at the isp connector on the programmer...
the Vcc and Gnd pins... but it must be very low-amperage as it
will not power the AVR.

The voltage at the USB connector on the programmer is 5.1v

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While I do not have a schematic this info may help you... some of which is an educated guess..the USB interface in Manual Diagram 3.1 is more than likely the FTDI usb/uart chip FT232 www.ftdichip.com..that site will show you alot about how to interface USB to a micro...the info you may wish to focus on is how the ftdi chip can both regulate and switch using an external FET the power to the external circuit..in this case it probably powers the avr on the pcb and the voltage convertor as represented in the block diagram. My guess is that the lower left hand side of the pcb as illustrated in the manual is the circuit of interest and probably similar to the FTDI app notes. This is the side you want to grab the voltage you need for the external AVR but you should obviously take some precautions. Typically when you first plug in a usb device it should consume only a small amount of current so it can enumerate properly then after enumeration it can switch a larger load on (this is the very abbreviated version of the process)...this should not really be a problem if you grab the power at the right point in the circuit and you watch the current. I do not believe the VTG pin is the one you want to grab without modifying the device..Refer to 3.2 and 3.4.1 in the manual....VTG is used an input to the onboard voltage convertor to tell it what voltage the TARGET AVR is operating at..this programmer supports TARGET voltages from 1.8 to 5 volts ..it only draws a small amount of current FROM the TARGET SUPPLY probably just for the level shifters and the ref to the voltage converter....the picture in the manual is so fuzzy it is difficult to glean more info from the picture..a good digital pic of the pcb both sides would probably reveal more ...I feel sure what you want to do is possible , but it may take just a bit more discovery on your part before you actually heat up the iron...onward thru the fog

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Quote:
is more than likely the FTDI usb/uart chip FT232

Yes, That is the chip between the two crystals.

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digital pics are great! assuming this is not a multi layer and for the cost I doubt it is you can draw a schematic from these..I think you can tell what is dcc so probe the vcc pins on the 8535 and the tiny2313 pin 20 to see if they are 3.3 or 5..reste pin on pin 1 of the 2313 is reset thru a pullup to vcc wiht a cap on it...res should be traced back to a tantalum below it..thats the power supply poin to probe...I think the dc to dc converter is in the lower left corner .I can not see any marking on it..do you...since this is not an isolated converter one or more of its leads should go to dcc...another should be an input which would be associated with a cap of which there appears to be two... I know the one on the right is but the one on the left possibly..some of the newer low current/voltage dc to dc converters do not require a catch diode which I do not see

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trace vtg pin to see where it goes..your measuremnt of 4.5vdc on this pin is somewhat curious..I can not see clearly the connections to what appears to be a tant cap by vtg pin...my guess is that the vtg input pin may go to an an analog input on the 8535 so the pc program can read the target voltage...possibly thru a resistor with a cap to dcc...if you can not tell which are caps and which are resistors refer to manual..in the color illustrations apparently brown squares are where caps are and blue squares are where resistors are for the most part....black squares...tant caps with a polarity indicator..the object is to see what components are connected to VTG since that is the pin I assume you wish to power the target VCC (+5) to..my next guess is that after all this you will find no problem..but you might want some protection on the vtg pin on the target isp pin....possibly a polyswitch, small res, but.... curious when this widget is not strapped to a target does the pc program screen fig 5.6 of manual that shows the target voltage give a reading? i think you are on the right track and you get extra * for researching before smoking it...most seem to smoke first and ask why later!!!! I am off in the fog........

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:idea: a few more thoughts to consider

Since the vtg pin is an input to the programmer from the target VCC so the programmer knows what the target voltage is and can drive the isp output pins to the target at the proper level and report that voltage to pc
AND since this programmer is designed to program a target at any voltage between 1.8 to 5 v
Strapping usb 5 vdc to vtg pin could present several issues...especially if you intend to connect this programmer to any other isp connector other than your zif

Consider target voltage at some voltage less than 5 v connected to VTG and USB supplying 5v to VTG!!!
Even if both target and usb at 5v ...power sequence and two current sources an issue wthout proper design...lastly what if you put the target device in the zif incorrectly?
If you plan to ONLY connect this isp programmer to your zif socket then the issues can be easily resolved.
Hope some of this dribble has helped..... :)

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Thanks for the help bluegoo :)

I am going to add some jumpers on the board that holds the zif socket
so that I can set the V+ to 3.5 or 5v... I have a bunch of 1n4001 diodes
that I can use to drop the voltage. Mostly all I need is 5v but once in a
while I program an Atmega169 that needs 3.5 (the butterfy) I will also
have a jumper to allow me to kill the USB 5v connection to the 10pin
cable so that I can program an external board that has its own power on.

I will post pictures of the completed programmer board as soon as I
finish it and give it a good try-out (if I don't blow it up)