Using PL2303 based USB to TTL converter with Arduino

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I bought these USB to TTL converter from ebay (Link ) for $1.5 a piece. I thought these would be good for programming arduino. As I keep building arduino projects and wanted to keep the USB connectivity with few of the circuits. I did not like the idea of plugging the FTDI cable to every project. instead I wanted to keep a B type USB connection with my project.

So I thought of giving a try to these super cheap USB to TTL converters.

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But these converts do not have a reset pin. As you can see, it has 3V3 pin but not the reset pin. After some search online I found that the DTR pin 2 on the PL2303 IC cab be used for Arduino auto-reset. We need to use a 0.1 uF capactitor and connect it one end to the Pin 2 of the IC and the other end to the Arduino auto-reset. So I thought to go ahead and mod this. it would require some soldering and a 0.1 uF capacitor. I could also get rid of the 3.3V pin and reuse that for the reset pin. As for my projects I did not want the 3.3V pin. If you want to use that, you may use the Reset pin separately. Here is quick tutorial on how to do this Mod.

What you would need:

  • PL2303 Module
  • 0.1 uF Disk capacitor. 
  • Intermediate Soldering skills
  • ( Optional ) Heat shrink tube

I had bought 5 of these from ebay. the Modules are covered with transparent heat shrink. First Cut off the heat shrink to expose the circuit.SANY0800





 

 

 

After that,  desolder the capacitor on the 3V3 pin. Also cut off the trace that connects it to the 3.3V on the IC. If your Module looks different than this one, look for the 3.3V pin. In case you cannot cut the trace, just leave it and use a tinned wire for Reset pin.

SANY0805After cutting the trace and removing the SMD capacitor, I soldered the 0.1 uF capacitor from the IC’s Pin 2 to the 3V3 pin.

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Use a heat shrink tube to cover the circuitry. This will also secure the Capacitor. Here are the final results. I tested it with Arduino and it worked flawlessly.

SANY0810I hope it was useful to you.

Cheers!!!

 

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Posted in Arduino circuits | 2 Comments

Tweezers for probing using cheap Kelvin Clips

SAMSUNG

I wanted probing tweezers for small SMD components on boards. Something like smart tweezers that I can connect to a multimeter. I had an extra  Kelvin clip, that I got very cheap from ebay ( link ). You can easily get them for $5-6 a pair. I thought, why not to modify this into a tweezer. Here is what I wanted to achieve.

  • Reverse the Spring action so that Clip tips are normally apart instead of being pressed at each other.
  • Decrease the spring force. this will make easy one handed operation.
  • Sharpen the clips nose for better contact with small SMD components.
  • Insulate the probes to avoid touching around unnecessarily.

The results I got was better than what I was expecting. I could probe small SMD components. I could easily probe 0402 size ,though I only wanted it for 0805 sized components. I thought of sharing this with others as it may be helpful.

Kelvin Clips

 

  1. Step 1 : Disassemble. I disassembled it easily. you only need to press the split plastic bushing on both sides.

I separated the clips to find a spring with long ends. I had to reverse the spring action by mounting the spring in opposite direction. The length of the spring was more that what would fit in opposite direction. So I thought of cutting it first. But I had a smaller spring in my junkbox, which was of a proper size that I needed to mount in these Kelvin clips. I had scored it from a floppy drive few days back. So I thought to give it a go. I had to bend the new spring so as to make it easy to put in the clip in opposite direction.

The one on left is the spring from the clip. the right one is from the floppy drive.

I had to Bend the new spring in way that it resembled the original spring. The right angled bend at the end of the keeps the spring straight when mounted inside the clip.

 

 

  1. Step 2 : Replace the spring. I replaced the spring and assembled the clip back so that the spring action is opposite. Instead of pushing the jaws inside, now it is pushing then outside. More like a tweezers now. I tested the tension was right for one handed operation.

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As the spring was smaller than original one, it was prone to slipping out of the clip from the front, I drilled a small hole and put a screw in between to hold the spring in place.

 

 

  1. Step 3 : Make it sharper.I sharpened it using a file. The jaws were made of copper. So it was easy to file it. After some filing, it was now having nice sharp jaws, suitable for probing.

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I also had to angle the jaws so that the tips of the jaws touched each other. One thing i learnt is that keep the jaws together preased tight, and then file it to make a sharp tip. this way, they are an exact match and bite well.

The sharp tips helps in poking on PCB as it can easily pinch through the solder mask, or oxidation on the parts terminals.

  1. Step 4 : Insulate: I took some heat shrink tube and put it on the jaws of the clip and then heated it with a hot air gun. It now fit nicely on the jaws, exposing only the tip enough for probing.

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I used heat shrink tube of two diameters. One for the metal part and another with greater diameter for covering the plastic part and the metal.

I also colored one of the sides of the clip black, so it is easy to understand which side is the probe ground / negative terminal as connected to the Multimeter.

 

Step 5 : Test. Final part was to test it. I tried probing various sized components on a a board. here are the pics.

Some more pics. Here are some more pics of the assembly.

I am pretty satisfied with the results. I hope this was useful to you.

Cheers!

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Using a wifi router as a network switch / hub

This post will help you do the following:

* Use a wifi router as a switch or hub.

* Use advanced features of DD-WRT. its a custom firmware for wifi routers. link

I had been using a Linksys wifi router for long. Then I switched to a new router from Belkin. As I have a complex network at home of Desktop, NAS Drive, Media Player, XBOX, PogoPlug etc… I need a lot of LAN connections to make everything work. Long story short, here’s how you can use a router as a switch.

The setup : My setup includes two routers. One being used for gateway to internet using a LAN cable based internet connection. Second one will be used as a switch.

 

1. Belkin n750 : As Primary Gateway

2. Linksys WRH54G Wireless-G Home Router. As HUB / Switch

 

 

 

Step 1: Login to the gateway router using web interface. Review the Gateway router’s settings. you would only need to get the correct IP address to use for the second router to be used as switch.

As given in the figure, I had my router set for IP address starting 192.168.2.2 to 100. For the second router to be used as a switch, you would need to set the IP address more than 100. e.g. 192.168.2.101.

Step 2: Login to the second router using web interface. its better if you are connected using LAN cable. I had DD-WRT custom firmware installed on the router. It gives lot of additional options to play with router. So, it would be worth if you install the custom firmware use link. Its an easy process to install the firmware. make sure that you follow the instructions. if you have a different router, it would be a similar process.

Disable the Wireless Network Mode. this may not be necessary but its better to just disable it. My router consumed 0.5 Watt lesser when wifi was completely disabled.

Step 3: Set the IP address of second router.

Set the Router IP as 192.168.2.101. This is also outside the range of primary router. Now for DHCP settings, select DHCP Type as DHCP Forwarder. and DHCP server as the first routers IP address. in my case its 192.168.2.1. set it as per your router settings.

With these settings, the second router will take the IP address from the first router. You do not have to use the WAN port at all on the second router. only use the four LAN ports as you would for a normal HUB/ SWITCH.

Thanks for reading…

Cheers!!!

 

 

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Transparent Power Brick

I had built a power adapter for my in-laws earlier using a white box to power a wifi router and DSL modem. It did work well at that time, but it eventually got damaged due to melting of the box by the transformers getting hot. While I could have fixed it by replacing the transformer, this time I wanted to build a better power brick. I wanted to let go the heavy / ugly transformers and instead use switching power supplies I scavenged from power adapters lying around in my junk box. I also wanted to make it look cool this time so that won’t sit behind the computer table. So I thought about using a transparent (Acrylic) casing for it with guts visible. The final product looked good and also pleased my in-laws as it looked cool.

Here’s how I switched from ugly box to a transparent adapter.

The old box was meant to supply power to two devices.

1. A DSL Modem running with a 12V power supply.

2. A Wifi Router running with a 5V power supply.

 

Both devices had their own power adapters but they had gone dead. As there was already a shortage of power sockets near the computer table ( well, most of us face this problem ) I thought of putting everything in one box and also adding a socket it for extra plug. This way, it can take care of three devices with one socket. Built some three years back, I was happy with the results, as I shoved all the parts in one nice box.

 

But over the time, the white box gave away to the hot transformer. The box melted and it caused a short circuit killing the 12V supply. I tested and found that the transformer was dead. So, I thought of replacing it. Then it occurred to me to build a better one this time. Use switching supplies instead of transformers. As I scavenged my junk box, I found everything I wanted.

 

Building the Box – Raw material : I had 2 hours to finish this small project, as without the adapters the internet was down for my in-laws without power supply for DSL modem & wifi. I took the dead white box and drove back home. I searched and found following items that I could put together for the new supply.

1) A Transparent box that an iPod Nano came in, as enclosure. I checked and found that it had enough room to hold two power supplies separated by enough space to avoid short circuit (again). Apple builds stuff with high quality material, so I believe the box will be pretty sturdy.

 

 

2) Few small sheets of PVC. to be used for building interiors.

No screwing, only using hot glue for this project to finish it fast.

 

 

3) A small night-lamp. To give it a glow. ( Who doesn’t like a glow ). It will also serve as the prongs for the power brick. I tested and found the prongs were designed well to fit snugly in most wall sockets.

P.S. In India, the wall sockets/ plugs come in variety of standards. I mean most are similar but I hate the minor differences that causes plugs/ adapters to fall off very often. So its got great value if a plug fits the sockets well.  

4 ) Power supplies. I cracked open two working power adapters that were lying around; were earlier used in a 8 port switch & a PPOE router that I don’t use anymore. I confirmed that the current ratings of 1000 mA  at 12V & 5V respectively were good enough. I kept the cables with plugs that will be later used.

 

Building the box – Assembly : After collecting everything, I got started with a hot glue gun & soldering Iron. I know, you may hate Glue, but I had planned to finish it in one hour. I also was fascinated by idea of giving it a hand made look. Besides, nothing is as easy as just using Glue to put things together for electronics projects.

I measured the box on how to put things together. As I wanted the guts to be visible, I decided to mount them side by side with components showing outside. drill holes in the box for the cables and mount the prongs directly the box. It will make it like a standard power brick that can be directly plugged in.

 

I cut the sheets to form two cavities for both the PCB’s. Glued them inside the box. I tried to avoid gluing the outside transparent areas as much as possible but couldn’t do it well.  I believe that the glue is a creature with its own brain and will. it will always stick to places where you don’t want to.

Anyway, it was not too bad. I drilled holes for the plug cables. Inserted the wires from the holes & then soldered them on the PCB’s outputs making sure that polarity is correct.

Then I disassembled the night lamp. it was secured by few Philips screws. it had three parts; prongs with circuit, a translucent body and top cover. I carefully soldered two pieces of wires to the direct 220V power on the PCB. Cut holes on the box so that the box can be sandwiched between the two parts of night lamp.

 

I drilled a hole on the back plate of night lamp to take the wire out of it. These wires were then routed from the transparent cover of the box to be eventually supply 220V to the two power supply circuits.

After doing so, I put the parts back together and tightened the screws.

 

This is what the end result looked like. The cover can be put back on the main box.

 

 

 

 

Final Assembly : I was happy to get this far in first hour. I wished to rush from here, but took time to make sure the assembly was correct and there was no loose connections/ soldering.

 

As you can see, the cover was put back, the wires coming from night lamp were soldered to the two power supplies. The cables with plugs come out of holes in the box. I added some more glue near the holes to hold the wires and not stress the circuit solder pads. I tested everything with a multi-meter and it looked ready to go.

Finished Product Comparison : The finished box looked nice and worked well. After testing the Voltage on the two plugs, I marked the plugs with 12V & 5V so that they do not get plugged to wrong devices.

Here is a comparison of the old and new power supply.

Thanks for reading…

Cheers!!!

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