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Support Forum » Another USB Interface

May 18, 2009
by digitalpenguin
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I'd like to get my hands on another serial interface and usb-to-serial adapter for an additional project. Have you guys, the Nerd Kit team, thought of selling these individually in your store as well? (I'm happy to support you guys more through additional sales!) If not, is there a Digikey part number that you've used and/or recommend?

The usb-to-serial adapter is easy enough to get but I haven't searched for the rs232 kit yet.

May 18, 2009
by n3ueaEMTP
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@ digitalpenguin, I had the same question. I currently have 4 projects running simultaneously. I also have built a number of projects for my friends. I went to Digi-Key and ordered some Schmitt triggers. Its the 14 pin IC on the programming header & built one into each of my projects. That way, I don't have to open the box to reprogram the MCU each time. Of course this only works if you are make small changes to the program. The schematic for the circuit is in the NerdKits manual. It is however just as easy to duplicate the one that came with your kit by looking at it.

I paid less than $20 for a tube of 25 (including shipping). I would have bought them from the NerdKits staff (if you email them, I'm sure they'll help you out) but the only ones they had at the time were already soldered to the PC boards & I wanted to put them directly on a breadboard.

Hope this helps

Chris B.

May 18, 2009
by digitalpenguin
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Thanks n3ueaEMTP, your solution does make sense long term ... I was really just being lazy. :)

May 18, 2009
by Kevin
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I built one with a Schmitt trigger that I had in my parts kit but it does not work. Checked the wiring about ten times. I used a 74C14N slightly different part num than the one in the nerd kit CD74HCT14E but looking at the data sheets it should be ok....no?

May 18, 2009
by n3ueaEMTP
n3ueaEMTP's Avatar

@ Kevin, Not really sure how to handle that one. I emailed the NerdKits Staff & they directed me to Digi-Key so I just followed their instructions. As far as the wiring, I tired the schematic and ultimately just copied the programming header. It took me a few attempts before I got the two sided circuit board onto the breadboard in a working condition. Anyway, if you'd like I could post a picture of my completed circuit.

Hope this helps

Chris B.

May 19, 2009
by mrobbins
(NerdKits Staff)

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Hi Don,

I just e-mailed you some instructions on how to buy those from us. In general, we are happy to provide extra parts beyond those listed on the store -- we just haven't gotten around to adding them yet. Just send us an e-mail letting us know what you want, and we'll send a custom PayPal invoice back. Let me know if you have any questions!

Mike

June 18, 2009
by BobaMosfet
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Kevin,

Make sure you got the part number correct on the trigger IC (CD74HCT14). Mine didn't have an "E" at the end. I grabbed the datasheet for it, and recreated a schematic of their Serial Header, and honestly, it's one neat little device.

Note the 10pF capacitor also being used as a bypass capacitor, and the way the CD74HCT14 is wired, it inverts the bits before sending to the serial port, and the inverts them again, prior to shoving them through an LED.

There is one trace that is difficult to see, it's directly under the trigger IC, and ties pin 7 to GND.

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