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ArcticMyst Security by Avery

Some things I've learned while making drivers.

Hiemal

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Hey all, I wanted to go ahead and share some information I've learned over the course of many months, while making and designing the E-drive.

Well, first off, it's definitely hard. Drivers are not something that are easy to pump out, for a variety of different reasons.

You need to research for different IC's, first off to figure out what the basic framework needs to be for the driver... There are so many different Ic's out there by a huge number of manufacturers, and all of them have different pros and cons.

Price, size, ease of use, mode, current capability, voltage capability, features, etc.

Then you have to learn how to use Eagle, or some form of PCB designer. Eagle has a pretty decent learning curve, but once you get it down it becomes pretty second nature to design a PCB using it. You have to double and triple check the boards to make sure that you didn't forget any connections, and to make sure that nothing is too close to something else.

And even then, occasionally mistakes will be made and a certain revision may need to be thrown away. I think in the process of making the E-drive, I went through almost 10 different board revisions.

Then there's the topic of finding parts for your driver; Capacitors, resistors, inductors, mosfets, etc, they all need to be sourced from a company like Mouser, Digikey, Newark... pricing is definitely a big player here. If you search around you can easily find the best pricing for a certain component you need.

Then there's reflowing. Putting solder paste on the boards can take a bit of time especially if the main IC is a pain (like the E-drive's). You have to use it pretty sparingly, don't ever just glob it on. The surface tension of the solder, once it reflows, will pull the parts into place, which means that although alignment is important you don't need be 100% on the dot with it.

Also, when reflowing, make sure you don't have the oven on the temperature you're reflowing at on the dot. Why? I found if you try this, there will be a good chance the parts will "pop" off the board due to thermal stress. Or, they'll "gravestone", where one side will reflow right but the other will flip straight up into the air.

Then once you have the parts, and the final revision, there's always testing and probing the drivers.

I've found a few things to keep in mind when testing a driver...

1. Always, ALWAYS use thicker wire for the main power connections. I found that when boosting the driver will draw a lot of current, as expected, and during my testing I noticed JUST the leads to the driver were dropping .7 volts!

That's quite the loss there so I switched it out with a much beefier cable and found the driver to work a lot better, less heat and overall it was happier.

2. Make sure your DMM connections are reliable. When testing I also found the connections to the DMM weren't spot on, and I had to end up using a completely different DMM to measure.

3. When testing a driver, try not to use a DMM in series with the load. This may go hand in hand with 2, as I found the DMM wasn't reading currents correctly and was skewing them by almost 400-500 mA... Fixed the connections, and measured the resistor voltage drop, and found the readings were correct.

4. Make sure you're using good batteries. I initially was using some very...crappy li-ion batteries, and well they couldn't handle the load and thus I couldn't test the driver very well. I got fresh ones and have no problems now!

5. Always experiment! If your driver isn't running properly, or has spike problems, try swapping out different values of components with them. You'll be surprised what 0.1 uF and 0.001 uF capacitance difference can do to a driver.

6. Don't get frustrated. Testing a driver takes a lot of time, and well, it can be frustrating when it doesn't work right. Always check connections to make sure nothing isn't goofed up, check the batteries, check the test load. Rule out things!

Oh, and then there's just, time. All of this takes a LOT of time. Be prepared to spend hours testing, to spend DAYS designing, and hours again finding parts and sourcing them for your driver.

I hope this helps out some people who may want to make their own. Also, don't think that it's all just boring either. You definitely do learn a TON, as my experiences with it have shown, and well it is definitely a rewarding experience when it finally works as you had designed it to.
 





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1. I think you and I are the about only ones that think 26AWG is unacceptable for high current :(

4. Or even better, a bench power supply. Ties in with #6: "rule things out"
 
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Blord

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Define high current. How much current does the 26AWG wire need in order to be limited factor.
If only wires are used between the diode and the driver I would think that would be okay.
Of course the shorter the wire the better.
 
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I wouldn't put anything over 1-2A through it, but that's not to say 1.99A is fine and 2.01A is too much. As stated above, larger is better. Wire is dirt cheap, especially in the short lengths you use here; there's really no reason for using teeny stuff (except it's easier to manipulate, I guess). You're just wasting energy.
 

ARG

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It's easy enough to calculate the resistance of a strand of wire. Set your variable PSU to 1A (Check it with a good DMM) hook up either end of the wire to the PSU and measure the voltage across the wire. 1V=1Ohm resistance.

Then you can use ohms law and calculate how much voltage the wire will drop.
 
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I miss building :/ Maybe when classes are done, ill put more time into it and see what i come up with :p Im sure my OCD will make perfect results...
 
Joined
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You can also look at tables for the ohms, suggested current loads, etc. I tend to use hookup wire (22AWG) or Ethernet wire (24AWG) for connections, preferring the former because my mechanized wire strippers work well with it. On my manual strippers, I had to actually file down the washer that helps set the stripping size to handle the Ethernet wire. I can't imagine what a pain it would be for 26AWG. Ironically, I've got a nice 30AWG wire stripper for wire-wrap (recently acquired!); so 26AWG is the odd-man-out.

Texas Instruments also has good guides on circuit board layout. Just search for "Texas Instruments PCB" on Google and you can find links to their guides.
 

Fiddy

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troll_icons_2_28891_7697_thumb.png
ive done a lil bit of looking, but haven't found some with that nice insulation and as flexible.
 

gillza

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@ Le Quack ha! you got there first. I was about to post the link for the black one.
 
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