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1  Using Arduino / General Electronics / Broken pot, don't know how to read markings. on: August 18, 2013, 09:42:02 am
Hey there, so I've got a potentiometer here that came off an airsoft gun. It's clearly broken. Broken to the point that I can't measure a resistance on any of the pins (the thing saw some heat for god only knows what reason).

Its apparently part of the circuit for adjusting the guns ROF. And test firing the gun with an assortment of pots I have, I'm thinking it should be in the ballpark of a 5k.

Reading the pot however its labeled as.
B is the signifier for linear I believe, which works for me.
5k also works.
but the hells with the 4?

Supposed to be a 5.4k or something? I just wanna get the right part so the thing doesnt break the gearbox down the road and the kid blames me. (though with how he treats this thing, I'm surprised hes had it for 3 years)

If anyone can set the record straight on what the B5K4 tag means, it'd be appreciated.
2  Using Arduino / General Electronics / Re: Surge supressing for Solid State Relay? on: July 19, 2013, 02:50:17 pm
Sry for bumping my own post, but that project got sidetracked at work for a while.

Just wondering, would this be a good diode to use as a flyback? If not why? Cause I've read a bit and I still can't understand how to properly spec out a diode.

Thanks for the help everyone.
3  Using Arduino / Project Guidance / Re: Electronically actuating a keypad button with arduino on: July 19, 2013, 02:40:10 pm
Yeah so tried calling the manufacturer a couple times, but they don't seem to want to talk to me much, I left the phone on speaker while on "hold" for 48mins 39 seconds before I said screw it.

Best thing I can think of pending that would be a mechanical relay setup (quite cheap, and you won't have to worry about the 5v vs 1.5v problem).

I'll Diagram it out a bit for you later, but heres the rundown.

Basically make a little box with 6 relays in it. Make an adapter that takes the wire that connects to the keypad and brings it into the relay box. Hook up the 6 relays to emulate pressing each button on the keypad, and have the arduino trigger them as needed. Sadly this will be a little bulky, requiring a second box and all. Also you'll have a higher power demand while working due to the relays (though they're only going to be on for a second or so so it shouldn't be bad), also you'll want flyback diodes for each relay (don't want to break your arduino pins).
4  Using Arduino / Project Guidance / Re: PI in arduino on: July 16, 2013, 02:15:35 pm
Doesn't M_PI require the math.h library?
5  Using Arduino / Project Guidance / Re: Electronically actuating a keypad button with arduino on: July 16, 2013, 01:10:21 pm
Hmm well so far no response from the manufacturer on the email. I get the feeling that the thing will take serial commands of some sort because it appears that in the first pic, theres a chip that has CTS (mayeb clear to send) on it. Looking at one of the guides about the keypad though it says that switch 4 isn't used, its for future features.

As far as teh 1.5v, that means you probably can't use a regular arduino transistor setup to trigger the thing (arduino would use 5v transistors. The arduino pros 3.3V, dunno how you'd get 1.5 without some silliness or mechanical relays.

You could do some servo thing, but that would be a bit bulky and easy to break.

6  Using Arduino / Project Guidance / Re: Electronically actuating a keypad button with arduino on: July 15, 2013, 01:52:05 pm

Thats correct. I want the arduino to produce the keys electronically. It would be ideal to have the arduino directly communicate with the dead bolt microcontroller (what is ucontroller?); but I wouldn't know where to begin to figure out how to do that. There are female headers on the motherboard that I think is for that type of purpose, but again, I wouldn't know where to start trying to figure out how to communicate with it. How would you go about doing that?

The header look like this.


Sorry, often microcontroller is shortened to uController. The SI symbol for "Micros" is μ (Mu), and its similar to a u, so people do what they do.

I shot off an email to the deadbolt manufacturer asking if they had and documentation on whether or not the controller would take serial commands. We'll see about that when they respond. But if you look up the arduino keypad library and read about that. It should explain to you the basics of how these keypads work (and a thing called multiplexing, where they use fewer pins to do the same amount of work sensing the button presses)
Looking at the keypad itself only pins 1-5 have anything to do with button presses (6/7 are for what appear to be LEDs to light the keypad up)
Now the way these pads work is the button has a conductive rubber surface on the bottom of each button. When its pressed, that surface hits the overlapping traces and creates a short. Depending on which keys are shorted at any particular time, the controller uses that to tell what button was hit.

So when the controller sees pins 1 and 2 shorted together, you get button 2 being pressed. When pins 4 and 5, you get button 5.
Your goal (if it doesn't take serial commands) will be to hook up some transistors, that your arduino will trigger in the correct series to connect each pair of pins for each button. This way the arduino is effectively doing the exact same thing as if you walked up and pressed the buttons yourself, BUT at the same time, you still have the option of using the buttons.

If it wouldn't be too much trouble, could you take pics of any other boards you pulled out of this thing, And if you can a real good shot of the controller board.
7  Using Arduino / Project Guidance / Re: Electronically actuating a keypad button with arduino on: July 15, 2013, 12:48:06 pm
So just for clarity. You have an electric deadbolt that uses a keypad, and you want to make the arduino trigger it with RFID?

Whats this about making the arduino press the buttons. SO like the arduino produces the keypresses electronically, or mechanically.

Electrically you could probably bring the 1-7 pins out. Then use transistors to trigger each pair as needed, (so 4 connected to 5 would equal S5 being pressed)

If you were willing to do some hacking though you might find that the keypads uController will take serial commands so it can be opened remotely and such, and if it can, that would save you a lot of trouble because then you just need a few Serial.print lines for your code.
8  Using Arduino / Project Guidance / Re: operating environment on: July 09, 2013, 10:32:55 am
from experience most things are rated to like -20 to +80 C. But you can go colder if you were to build a little heated case to keep the duino warm YMMV though
9  Using Arduino / Project Guidance / Re: Tracking on: July 03, 2013, 01:23:12 pm
Using an arduino as a webcam analyzing tracking system might be a little bit of a stretch. Maybe with a due's higher speed you might be able to pull it off, but 16MHz is rather unlikely unless your fine with refresh speeds less then 1Hz.

If you could modify the ball you want to track though with some IR emitters, a wiimote camera might be able to do an alright job. (100Hz refresh, good viewing angle, and it does the position resolution itself and just spits out coords, simplifies what the arduino has to do a lot)

Also not an arduino project but I recall seeing some people using a Raspberry Pi as a color tracking system for an airsoft autoturret, run off of a webcam. But even that was rather slow and only refreshed at like 3Hz (I gave them props though because it could accurately track and compensate for constant speed of a target and lead its shots. Had nothing to account for range though)
10  Using Arduino / Project Guidance / Re: UGV project with ebay components on: July 03, 2013, 11:04:00 am
At first I saw tank and arduino and I was gonna say go hydraulic, but hydraulics a little big for something a foot or 2 across.
If you have the space you can probably buy a nice pair of brushed DC motors that put out about 1/4 to 1/3hp to move aroudn your 30-40lb steel tank for a few hundred dollars each. If you are willing though, a couple lengths of 80/20 for the framerails, then tig welding the rest of an aluminum chassis onto the unit, the thing would probably end up coming out light enough that you won't NEED a really really big motor.

Also in other news, those tracks in the video are way too wide. Every one of those little pivots is even more friction, and sadly they're a pretty bad design. You could probably get by making a 3 wide track like that and building trackplates onto them. The reduced friction would greatly boost performance for whatever size motor your using.

When you said gear it down, that means it needs to have bigger second gear?

It means that theres a small gear on the output shaft of the motor, and a larger mating gear that goes to your track drive (or another small gear if your having more then 1 step of reduction)
so say your output gear has 20 teeth on it, and it mates to a 40 tooth gear, that means you'll end up with half the RPM, but double the torque. a 20/60 would end up with 1/3rd the rpm and 3x the torque
11  Using Arduino / General Electronics / Re: Surge supressing for Solid State Relay? on: June 24, 2013, 10:07:49 am

It matches the numbers on the relay we have
12  Using Arduino / General Electronics / Re: Surge supressing for Solid State Relay? on: June 20, 2013, 02:10:16 pm
Any reason why the SSR would have a small transformer inside of it then?
After dismantlement, theres a MOSFET, little transformer, and a board with an LED that I'm assuming does the optical isolation to protect the microcontroller thats triggering the relay.
13  Using Arduino / General Electronics / Re: Surge supressing for Solid State Relay? on: June 19, 2013, 01:41:35 pm
Also the HiPot test is carried out by applying 2000VDC to the A,B,C nodes, relative to the core (and some thermistors built into the unit)

Are the coils isolated from the SSR when the HiPot test is carried out? If so, how? If you are relying on the selector switch contacts all being open when the HiPot test is carried out, then you need to use a selector switch rated for 2000V.

Yes the HiPot test is completely separate, often happening a couple days before the polarity test that this box is for

I've been thinking to opt for a flyback diode, however I wonder where exactly to put in. I could attach it across the terminals of the PSU, or the relay (or perhaps I could throw them everywhere, flybacks for everyone)

The flyback diode should be connected between the SSR output/selector switch junction and the battery -ve terminal. That will protect the SSR from negative voltage transients. You might want to connect a 100V TVR diode there as well, to protect the SSR from positive voltage surges during the HiPot test.

-ve terminal? Negative? iight then. About how big of a diode should I use though?
14  Using Arduino / General Electronics / Re: Surge supressing for Solid State Relay? on: June 19, 2013, 11:50:01 am
I don't find your description of the arrangement very informative. Can you provide a schematic? How was the HiPot test carried out?

If you use the SSRs to break the 5A current flow to the coils, you can expect a large inductive spike, quite possibly more than 220VDC depending on the inductance and capacitance of the coils and the core material. When switching an inductive DC load with an SSR or any other device, you should use either a flyback diode (possibly with a resistor in series, if you need the current to decay faster), or a R-C snubber network (but that may not be practical with a 5A 15V load).

Sorry about that but I've been nowhere near a scanner or camera with which to upload a schematic, and the majority of my work is away from computer as well so I haven't gotten to make a proper schematic on there either. I'll throw a crappy drawn one up now, I'll come up with a better cleaner one later.

Also the HiPot test is carried out by applying 2000VDC to the A,B,C nodes, relative to the core (and some thermistors built into the unit)

What's limiting the current?   Are you sure it's limited to 5A?

I don't understand the capacitance either...  I agree, we need to see a schematic.   2000V from a capacitor across the SSR will probably kill it.   

If there is a capacitor across where the high-pot voltage is applied, you can get "unlimited" current when it's discharged, just as you can get "unlimited" voltage when you break the current path through a coil.   

I'd say you need to discharge the capacitor as a routine part of high-pot test, and I'd say discharge needs to be an automated part of the high-pot test to protect both humans and the SSR.

You might consider using a regular 'ol mechanical relay.    Mechanical relays are generally more rugged and more tolerant of abuse.    A solid state relay can last forever if it's not abused but it can also be killed instantly.   

A mechanical relay will eventually wear-out, but it's usually cheaper to replace and it's usually in a socket.

You might need a relay driver to power the mechanical relay coil, depending on what's currently driving the SSR.

The current is primarily limited by the resistance of the inductor coils themselves. But basically its hooked to a power supply and the operator dials the voltage and amperage to 15@5 when hooking up the first unit and then keeps those settings throughout the tests. It is able to jump a bit over 5A from unit to unit, however if one were far enough out of spec to have that drastic of a change, it would have been caught at an earlier test.

Me I don't understand the capacitance either. Checking it with a voltmeter on about all the points I can't find a C higher then 200fF which really shouldn't amount to anything.
On the automation side of discharging the unit, I've thought about having our testing bed pull all terminals to ground after the full test but (in the developer's infinite wisdom) they never added a feature like that.

As far as the mechanical relay, the boss says no. (for now, probably after another relay breaks it might be a doable compromise)

Controlling inductive loads with A SSR can be very problematic as the resulting voltage and current go out of phase with each other and that can cause major problems with turning on and off of the internal triac/SCRs. Carefully calculated and sized "snubber" circuits are the general solution for using SSRs with inductive loads. Or go with a good quality electromechanical relay instead.


Yeah DC only for tests, the unit is operated in DC as well. As far as a snubber circuit, I looked them up, but that whole carefully calculated part gets kinda in the way (ME intern, not EE, which leads me to wonder why I'm the one fixing this also)

I've been thinking to opt for a flyback diode, however I wonder where exactly to put in. I could attach it across the terminals of the PSU, or the relay (or perhaps I could throw them everywhere, flybacks for everyone)
Note in the schematic, the selector switch is rated at 125VAC@25A, though it is of much better make then the relay is. The emergency stop switch is also rated for 125VAC@25A, but is kinda cheap. Neither of these have failed (yet)
15  Using Arduino / General Electronics / Surge supressing for Solid State Relay? on: June 18, 2013, 02:56:24 pm
Hi there. So I'm having a problem with a couple SSRs in a test box I built dieing.

Basically, this box (and a power supply) is used to charge a large inductor coil. For that role it works great. Its actually 3 inductor coils (A B and C) that are all attached together at one end. The box is used to direct current as needed (A+B-, A+C-, B+C-). Used to check the polarity of the unit at a number of points. Works fine for that. The solid state relay in question is used to switch the 15V@5A that is used to charge the coils during the test. The relay we are using is rated for 220VDC@25A.
Clearly we should be safe with the rating of that relay (even assuming a voltage spike from when a coil is discharged)

My thought for why the relay has broken is that it is used to check the inductor array AFTER a HiPot test (2000VDC). We know for a fact that there is a bit of capacitance to the unit (if you touch any of the 3 A,B,C terminals together or one of them to the core, it'll give you a little jolt). I'm guessing that when the unit is hooked up to the testing fixture, that charge that the unit holds is giving a little jolt to the relay, and after a few weeks of operating, bye bye relay.

So I'm working a couple angles to try and counter this. Aside from a manual way of shorting all the terminals to a ground to discharge them first, any suggestions on a surge protection method that could be added to the relay?
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