Succesfully fried the 74AHC125 buffer chip

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robertb17
 
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Succesfully fried the 74AHC125 buffer chip

Post by robertb17 »

Hello,

I built the USBTinyISP and it seemed to work well. I got the driver installed on a 32bits Win 7. Green light comes on when hooked up to a usb port. I also built a Dev board for AT89S52 chips which came as a kit. I hooked up power to the dev board (6V) and connected the SPI cable to the 6 pins header on the dev board. (pin1 matching pin1). After an instant, I heard a pop and got magic smokes coming out of my USBTiny. I unplugged everything and opened the case and saw burn marks on the plastic of the case where the buffer chip is soldered.

I am not sure if anything else has been affected by my experiment but it doesn't look like as the driver still load when I connect it.

I went to a not so local electronic store and they didn't have that particular chip. Instead, they had the 74125 and the 74LS125 ones. I got one of each. Looks like the pin-out are the same. Anyone could confirm that these chips are equivalent to the 74AHC125 as stated by the staff member in the store suggested?

The dev board I am using is "DIY AT89S52 Microcontroller Development Board Set for Arduino (Works with Official Arduino Boards)" from dealextreme. There are no specs anywhere about the SPI pin-out on the board but being SPI (6 pins header), I thought it would be standard. And I did not think the power from the power supply on the board would flow to the USBTiny either. I was thinking that the power supply would feed the board and the AT89S52 as well as the power from the USB device... I read the forum section about USBTiny and saw it not being compatible but I was expecting no more than seeing a tad bit of read light flashing and simply get an unrecognized signature from the chip at worst. I thought wrong. (using AVR Studio)

So, are the 74125 and 74LS125 compatible with 74AHC125? And should I worry about other components if it gets the green light and load the driver in Win7 when hook it up?

If someone can enlighten me also about providing power to a dev board while hooking it to the USBTiny to program the chip on that board... Is it a no-no, is it supposed to be possible?

Thanks for your help.

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adafruit_support_rick
 
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Re: Succesfully fried the 74AHC125 buffer chip

Post by adafruit_support_rick »

According to this post, the 74LS125 will work:
http://forums.adafruit.com/viewtopic.php?t=5555

Pikachu
 
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Re: Succesfully fried the 74AHC125 buffer chip

Post by Pikachu »

Never apply power when programming

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schmartguy1
 
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Re: Succesfully fried the 74AHC125 buffer chip

Post by schmartguy1 »

74125, 74LS125 and 74HC125 are functionally equivalent.

the "LS" stands for Low Power Schottky
the "HC" stands for High Current output.

simply, an "LS" is not a substitute for an "HC". they must match the circuit requirements. typically you get either higher speed (low power) or more drive but slower.

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