UPDATE: You can find a brief entry on Adafruit blog, thanks!
UPDATE: You can find this project on here.
Hi all! After some time out, due to some hard work, I’m here again with a ‘one weekend’ project. In my case, with three children. I'm sure it can be done in one afternoon! I want to start some projects with Arduino and IoT, so the first things I need is an Arduino board, an Ethernet shield and a switch to connect it to the net. Also I need a power supply for the Arduino board, and I think that, rather than use an external power supply, it would be better to modify the switch to add a USB power port that can power the Arduino board. I’ve got at home a TP-Link TL-SF1008D, a simple 8 port 10/100 Mbps switch. So, let’s open it and add it the USB port!
Break DownThe first thing we need is a Philips screwdriver to open it. Here’s a view of what's inside:
I’ll add the USB port in the back, near with the RJ-45 connectors. I chose a shielded USB-A receptacle that I have at home. It's from Molex (Part Number: 105057-0001). So, after removing the electronics from the case, I put the connector in place, mark and cut it with a cutter:
It seems to fit okay, so the last check is to mount the board again to ensure that the USB connector doesn't hit it:
Perfect! Once the mechanical part is finish, let’s go with the electronics. The switch is powered with a 9V external power supply. So, my idea is take this voltage and reduce it to the 5V for the USB port using any converter. The easy way is use a LM7805 or similar linear regulator, it’s enough and will work fine. But I haven’t any at home, so I use a PTN78000WAH, from Texas Instruments. What’s this? It’s a high-efficiency, step-down Integrated Switching Regulator that can give up to 1.5 A and has a wide input voltage, from 7V to 36V. It only requires two capacitors (Input and output) and a resistor to set the value of the output voltage (for 5V output, the required value is 21K). Obviously, it is over sized for this application, but it’s the one I have on hand! I mounted it on a breadboard, and also add a small 0.5A PPTC fuse on the output, to avoid damage the switch if there’s a short circuit on the USB port. The schematic and the breadboard are this:
Now it's time to wire the USB A connector and get the 9V input voltage from the breadboard:
With all the wires ready, it’s time to test to ensure everything is working fine before assembly it in the case:
Lights are good! Everything works fine, so it’s time to put all the elements in the case and close it. To attach both the USB connector and the breadboard, I use hot glue:
And finally, we only need to put the cover on the switch and enjoy with our new USB port!
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