Any electronics nerds interested in Arduino/Atmel?
 

I would like to build a little "automotive helper" board that does some common features that I always seem to need:

- Three relays for controlling dual fans in parallel or serial modes
- Interior light dimming, theater mode, etc.
- Fuel pump control (reduced pump speed at low engine rpm)
- Tach signal conversions (8 to 6 to 4, etc)

Stuff like that, likely other stuff I haven't thought of but could be easily added.

I can do that software side in my sleep but I am pretty poor with hardware. I can solder and breadboard but not design very well. For example, to trigger a relay I know in software I need to command an I/O line to go low. But you can't just drive a relay off a chip's I/O line, you need to actually excite a transistor which then fires the relay.

But that's above my pay grade. I couldn't breadboard it safely for you, because I only know the general principles and ideas.

I thought if there was someone out there that mastered their "300 in One" Radio Shack kit as a kid, perhaps we could do something together!

Let me know if you're interested. Not trying to get rich, just needed some circuits and thought it'd be an interesting way to learn something new!

Re: Any electronics nerds interested in Arduino/Atmel?
 

I'm working on stuff like that for my truck. I have designed and prototyped a vehicle speed compensated intermittent wiper control. And working on a headlight harness with partial-brightness daytime running lights. I'll be using plain sealed beam halogen bulbs, I've not been very interested in the non-DOT expensive non-stock looking bulbs with halos and all that jazz. Then there is the cluster light rheostat to PWM (pulse width modulation) LED dimmer to smooth the dimming and allow dimming all the way down to nothing with the headlight switch's rheostat. Switch-free capacitance touch circuit for a kill switch or to switch other things. One day I will add power windows of the type that use the switch built into the window crank, and I'll want to double tap that crank switch to make it control the passenger side window. I've got too many project ideas so I'm not getting anywhere with them, it's a slow process. All this stuff is relay free, using just transistors for the high current switching. Power MOSFETs, metal oxide semiconductor field effect transistors. Arduino can control all that stuff, and they are so cheap that you don't need to have a central controller for everything, you can use just a few pins of a controller chip for the individual project and seal it up in a project box and wire it up to the truck. Then select another project and use another controller. How about cruise control? I'm designing that in my head right now. I can help with hardware design.

Wiper controller example
Attachment 1787531

And the breadboard prototype of it
Attachment 1787532

Re: Any electronics nerds interested in Arduino/Atmel?
 

Cool! Maybe if I start with some real basics, I'll be able to follow along and others will benefit from my noob-level questioning!

Perhaps the most simple: control ON/OFF of a 12V relay. I understand I cannot drive the relay coil magnet directly, but this guy seems to do it. Is there support circuitry on the UNO that's being used, or how does he do it?

https://www.google.com/search?q=cont...TF-8#kpvalbx=1

Once I know how to do ON/OFF, I'll ask about power transistors. But let's start with ON/OFF!

int in1 = 7;
void setup() {
pinMode(in1, OUTPUT);
digitalWrite(in1, HIGH);
}
void loop() {
digitalWrite(in1, LOW);
delay(3000);
digitalWrite(in1, HIGH);
delay(3000);
}

Re: Any electronics nerds interested in Arduino/Atmel?
 

It looks like the guy in that video is driving the relay directly. I think that is using the Arduino's processor beyond the specs and may damage it. So you have the right thinking about using a transistor to drive the relay.

2N3904 is a common transistor and good to use in that situation. I like this web page for explanation of using a transistor for this.

http://www.ermicro.com/blog/?p=423

It also has the wiring for connecting a relay, and talks about a clamp diode (aka flyback diode) when driving an inductive load.

Getting into this, although it is not really possible to grasp everything that is in a datasheet unless you're an engineer, it is good to read them anyway. I had a manager a while back who encouraged me to read technical stuff, and he said you won't get it all at first, and you may never get it all, but each time you expose yourself to it you will gain a little more. Now a few years later, I agree. Google "datasheet 2n3904" or "datasheet atmega328p" to find and download the PDF manuals for the various components you will be working with. The atmega328p is the controller chip in an Arduino. At the very least those data sheets will show you what pins are what on the component. After you buy a 2N3904 transistor, you are going to need to know which pin is the base, which is the emitter, and which is the collector.

So, to just get down to the nuts and bolts of it, here is a doctored diagram from that ermicro blog I gave the link to above.
Attachment 1787627

You don't need a resistor in line with the relay, because the coil of the relay provides the correct resistance if you are connecting a 12V relay to your truck. 1N4001 is a common diode you can use as a clamp diode. And a 220 ohm 1/4 watt resistor is a common value to use to limit the current going from an Arduino pin to the base of the transistor.

You can get this stuff on aliexpress.com if you are patient about delivery from China. bags of 50 transistors, a few hundred assorted values of resistors, bag of diodes, breadboard, etc. each for a couple bucks with free shipping.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Thanks! I've been on vacation in Europe for a week and just got back - once I've de-lagged a bit I'll see if I can breadboard some kind of blinking light from what you've shared.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Ok, well thats pretty awesome. Are you going to be selling these?

Re: Any electronics nerds interested in Arduino/Atmel?
 

Well, let me get something going in my truck to prove it actually works. :-) Then we can talk about whether I can make extras.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Subscribing.

I find that I don't have much time for such endeavors but I have used my arduino and a few lines of code to make a signal generator to diagnosis some engine controller problems I was having.

Re: Any electronics nerds interested in Arduino/Atmel?
 

That page is a little deep for me, but it's in the right direction. But it's kinda written for people that already know the answer, I think:

"When we operate transistor as the class A common emitter amplifier usually we choose to bias the transistor (apply voltage on VBE and VCE) in such a way (Q-Point) that IC and VCE (output) will swing to its maximum or minimum value without any distortion (swing into the saturation or cut-off region) when the IB (input) swing to its maximum or minimum value"

So that's about where I got lost! But I understand in principle what is happening I think!

I'm not really clear on why the diode is needed for inductive loads. Is it because when the inductive field collapses it shoots a voltage spike into the circuit or something? I don't know anything about inductance, unfortunately.

Re: Any electronics nerds interested in Arduino/Atmel?
 

"When we operate transistor as the class A common emitter amplifier..." blah blah blah, that big phrase is noise in the article, because what we are more interested in is the next phrase "but when we operate the transistor as switch...."
What he's saying is when we use the transistor as a switch we want to turn it all the way on or all the way off.

I think you got it right. When you power an inductive device and then cut off the power to it, it sends a voltage spike in the opposite direction from normal current flow. So the diode absorbs that by essentially shorting across the coil contacts instead of letting the charge go through the transistor. Inductive devices are things with coils, such as relays, solenoids, and motors.

Incidentally, I noticed my truck has a diode across the terminals that attach to the A/C compressor clutch. That would be to reduce or eliminate sparks across the contacts on the compressor switch when it disengages.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Thanks for the help so far! I got the "transistor helping to drive a relay" circuit working as you described it above. I added an LED to it as well...

https://www.youtube.com/watch?v=CYKVmS9dIoE

Neither the chip nor the relay gets warm, and all seems well! It's not obvious because its out of frame, but the red and black probes go to my 12V power supply and the yellow and green go to the coil leads on the relay,

BTW, when I mentioned this to a friend, he said "Why don't you just use a solid state relay"? Will they support 30A?

Re: Any electronics nerds interested in Arduino/Atmel?
 

If you have a Pull-A-Part type place near by, you can salvage relays and sockets from newer cars. The one around here treats them almost as free stuff. A pile of relays and sockets will get counted as one misc $3 part. Your results may vary. One advantage of automotive relays is they usually include either a diode or resistor to suppress the inductive spike of the relay coil. I would still use the added 1n400x diode just to be sure. Hard to have too much spike and noise filtration. Vehicles tend to have lots of electrical noise wondering around. Something about 200+ amps of starter current and 50kv ignition sparks.

Another source for electronics stuff: https://www.jameco.com

You should be able to get a 30a solid state relay.

Re: Any electronics nerds interested in Arduino/Atmel?
 

I don't want to rathole on the esoteric, but since I visited the grave of Faraday last week (no joke- I did!) I should probably understand the diode a little better. I know why it's there, but does it happen because charging the coil for the relay magnet creates a magnetic field that collapses and shoots a big spike?

The reason I ask is that it sounds a whole lot like how to ignition coil works, so I'm wondering if it's the same effect.

In other news, sadly no pick a parts anywhere near me. Gotta be an hour at least (average bungalow now over $1,000,000 in my area so not a lot of wrecking yard real estate!)

Re: Any electronics nerds interested in Arduino/Atmel?
 

Yes, a spike after the transistor cuts off, you are right. A diode conducts electricity in one direction only, and does not conduct in the other direction. There is an arrow in the diode schematic symbol, that shows the direction current flows from positive to negative. So when the transistor is on and current is flowing from top to bottom in the schematic, the diode doesn't do anything. When transistor cuts off and the coil causes a more positive voltage to appear on the bottom contact of the coil compared to the top contact, the diode conducts to short out the coil and "use up" all the electricity in it.

Incidentally, back in olden days, somebody had to decide when talking about electricity, does it flow from positive to negative, or from negative to positive? In fact they had to decide what is positive and what is negative and what kind of symbols to use to picture it. Physicists have decided it is the flow of electrons in the wire that matters, and those flow from negative to positive. Electrical Engineers decided charges flow from positive to negative, and it has turned out to be the most common way of thinking about how electricity flows. That is a simplified explanation, but the bottom line it it doesn't really matter which flow you follow as long as you don't change your mind in the middle of reading a schematic. :-)

Re: Any electronics nerds interested in Arduino/Atmel?
 

Bingo on the ignition coil thought. Replace your switching transistor with points and add a secondary HV coil for the spark output and you have it. An ignition coil is a transformer that converts switched DC to HV DC spark output.

A computer controlled car replaces the points with a computer controlling a switching transistor that activates the ignition coil. That's why modern cars have things like crankshaft position sensors, so the computer knows when to fire the coil(s).

Re: Any electronics nerds interested in Arduino/Atmel?
 

Here's my next step - I should have used 3 MOSFETs but only had two on hand, so used three transistors to control the color drive on this LED strip. I also did a MOSFET version for the white LEDs.

So now I've covered transistors, 12V relays, and MOSFETs. I guess all that's left would be solid state relays and 120V relays!

https://youtu.be/rcm04NwtjA4

Re: Any electronics nerds interested in Arduino/Atmel?
 

Subscribing to this too.

I have worked a lot with Arduino stuff, and some with Raspberry Pi. Might be able to help out around here.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Well, as my next step I built a dedicated little board/circuit/computer based around the ESP32 chip. It does the following:

- When it boots up, it connects to the WiFi in my shop
- It then connects to the Internet
- It sets its clock from a web-based NIST NTP time server
- It then runs a web server and waits for requests
- When those come in, it measures the temp, humidity, and pressure in the air compressor closet
- It reports those in the web page
- It displays the current values on a little OLED display right on the chip/board itself

For a day or so it'll still be live here:

http://1969Pontiac.com:99/

...and here's a picture of the circuit. I was thinking it could manage the actual compressor if I wanted to go down that path! I might even do so if I can find a "soft start" controller for an AC motor that I can control somehow.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Does anyone know how I could control:

1) A large cooling fan (like 30A) with a solid state relay or transistor? What could handle that load? A big MOSFET in a can with a heat sync?

2) An AC motor like a compressor? I'd like to soft-start my compressor but again don't know what kind of solid state switch would bear a big 240V compressor!

Re: Any electronics nerds interested in Arduino/Atmel?
 

The annoying thing about heat sinking a power MOSFET is the tab is connected to drain, so that makes the heat sink have live power. So, isolated in a can like you mention would be good, but then you will probably have to circulate air through the can, perhaps with a cooling fan.

Regarding solid state relays, I have read cheap Chinese relays that are sold on Amazon and eBay are mostly counterfeit or fake, and have ratings that are not supported by the actual components in them, and are susceptible to fire or failure. So, I would recommend sticking with a supplier like Mouser, Digi-Key, Sparkfun, or Adafruit.

I am thinking a conventional relay may be best for those high currents.

Re: Any electronics nerds interested in Arduino/Atmel?
 

But for a fan or other load that you want to PWM, a mechanical relay doesn't respond fast enough. I know the Ford Taurus had a solid state fan controller, as does my 2015 Corvette, but I'd like new parts (not junkyard harvest if I can help it!).

Naive question - on the case being drain, does that change if its PNP rather than NPN?

Summit and Amazon carry a Hella relay that is solid state but appears to fit the conventional form factor and will handle 32A per unit:

https://www.summitracing.com/parts/h...SABEgIYEvD_BwE

So I could have three of those oboard:

1) Cooling Fan A
2) Cooling Fan B
3) Fuel Pump (duty cycled down below 2000rpm for example)

Re: Any electronics nerds interested in Arduino/Atmel?
 

Yes, true if you’re thinking about PWM a conventional relay won’t work. For something simple like switching from parallel to series would work with conventional relay.

That Hella relay looks like just the thing to use.

With MOSFETs they call them N-channel or P-channel instead of NPN or PNP but the concepts regarding application are similar. Both N-channel and P-channel mounting tab are connected to the drain.

That relay looks interesting, I wonder if that is a plasti-kote kind of insulating paint on the heatsink.

Re: Any electronics nerds interested in Arduino/Atmel?
 

I don't know if it's the right choice, but here's what I ordered to run my compressor:

https://www.mouser.com/ProductDetail...Qgm8BEGA%3D%3D

The compressor motor says 21A and that SSR is good for 30A.

I watched a few disassembly videos on discount 30A SSRs that are on Amazon and eBay right now and they're made using as 12A triac! So the triac is only rated for about 1/3 of the total device... so I bought a quality USA unit instead.

I'm hoping I can do PWM and slow-start the compressor motor with this, we shall see. I know I learned that most SSRs are actually "zero crossing" and don't change strate until the AC waveform crosses zero. So I ordered this one that is supposed to be instant.

I would have preferred someone made a "Large single phase AC motor speed controller" that I could just send a reference voltage and it did the work, but I couldn't find anything like that!

Re: Any electronics nerds interested in Arduino/Atmel?
 

Well I don't know about PWM for AC, I think it is for DC motors only, but I may be mistaken. It will be interesting to find out how it goes.

Re: Any electronics nerds interested in Arduino/Atmel?
 

I know... if I could time it to the 60Hz waveform precisely, I could turn it off an on for one waveform cycle at a time, but I'm going to be kicking it in PWM no matter where the waveform is right now.

In theory, it should work. But I have about as much theory as Benjamin Franklin...

Re: Any electronics nerds interested in Arduino/Atmel?
 

Look into a triac for AC PWM... https://www.google.com/search?ei=6ko....0.okNKgaixWr8

As for BJTs vs FETs they use a bit different terminology but the basic difference is the former operates on base current, and the latter on gate voltage. FET tech typically uses less current and higher voltage.

Re: Any electronics nerds interested in Arduino/Atmel?
 

It works for light bulbs, I'm just not sure about electric motors. I think if the PWM wave is fast enough (like 1000Hz at least) and the relay fast enough, it should work perfectly!

Since I have two phases I'd need two relays, though.

Re: Any electronics nerds interested in Arduino/Atmel?
 

I'm not entirely sure what you want to achieve.

Do you have a AC (alternating current not air conditioning) motor that you want to soft-start? Are you trying to drive DC cooling fans with PWM for speed control? Is the fuel pump supposed to be variable output?

Re: Any electronics nerds interested in Arduino/Atmel?
 

What is the purpose of soft-starting an AC motor? What does it achieve?

Re: Any electronics nerds interested in Arduino/Atmel?
 

Motors have high inductance, so when you power them on by just connecting it to line voltage, it is essentially a short for a small window of time. This causes a voltage drop in the system while the motor comes up to speed, and also means that the current in the motor is extremely high during this time.

Soft-starting drastically reduces the startup current and the current through the motor coils.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Although it sounds good, it is probably not a great idea to try soft starting a split-phase motor (cap start-cap run, or cap start-induction run) like is used on an air compressor. These motors pull a lot of amps on start up because they are high torque motors, and need to come up to speed quickly.
The type of motor usually used for soft-start is a 3-phase motor, and they are available with built-on or separate inverters/vfd module, so you can operate them from a single-phase power source

Re: Any electronics nerds interested in Arduino/Atmel?
 

I forgot to mention this.

Also, soft-starting reduces the average current, not the peak current through the coils.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Can someone explain cap-start? Does it store a bunch of surge energy in a cap for the initial inductive "kick" when the motor starts?

I decided not to monkey with my big compressor. I have a small desktop compressor I used for tires and air brushing that I will play with instead!

I built a switched outlet box with a 30A Craydon SSR in it to play with, we shall see. I searched and paid extra for a non-zero-cross relay. Normally they don't switch until the next time the AC crosses zero, which is OK as a switch but wouldn't work for AC slicing.

I've also been tinkering with a bunch of old retro displays and trying to interface them to modern electronics. Here are some of my results!

Little saga on the VFD display: it's a Japanese unit from Noritake and uses hand-coded timing loops to drive it that I could only get to work on the CPU they designed it for (which I'm not using because it's ancient). So for the $1.75 they cost, I dedicated an Atmel 328P (which it works with) just to controlling the VFD. It then exposes the standard LCD interface across the i2c bus so that the ESP32 can call it as if it were a local display. Works great, but was a bit of an investment.

I'm a software guy, so every one of these little wires is a victory ;-)

Re: Any electronics nerds interested in Arduino/Atmel?
 

You have to have some way of setting up a rotating magnetic field in a single-phase motor. Otherwise, the field just alternates without rotating. In a cap-start motor, there are 2 windings, a run and a start. The run winding is across the ac line, the start winding is across the ac line with a capacitor in series with it. The capacitor causes a shift in that winding (along with the winding being wound slightly different than the run) so that the field will rotate, to start the motor. On many motors, once the motor comes up to about 75% or running speed, a centrifugal switch cuts out the start winding, This is a capacitor-start, induction run. For loads requiring more running torque, a capacitor start, capacitor run motor is used. These have two capacitors, one for starting and one for running. The run capacitor stays in series with the start coil all the time. Air compressors and table saws often use cap-start, cap run motors. Another type of capacitor motor for low-torque loads like fans omits the start capacitor and has just a run capacitor. These are called permanent split capacitor (PSC) motors and they are very efficient.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Aha! That must have been what my EE friend at the power company was talking about when he was trying to dissuade me from doing this on my big 240V compressor... he talked about the potential of a centrifugal switch.

I need to read up a little more on single-phase induction motors, as with brushes and no moving fields, they're a little mysterious!

Re: Any electronics nerds interested in Arduino/Atmel?
 

So, bringing up this older thread to continue discussion. It's a slow process to work on the truck, but now that I finally got the air conditioning going I can think about other things. I was forbidding myself to work on other things until I got the darned A/C going. Here in Texas for a daily driver truck, A/C is pretty important for comfort. Although I usually roll down the window and stick my arm out, there are a few dozen days here where it is HOT.

Anyway back to the electronics and programming nerd discussion, I have in my truck's future the idea of power window for the passenger side. I have such a strong passion for rolling the windows down while I drive, if it's not too hot. And it rains a lot here. So when it starts raining, I need to pull over in a parking lot, put the truck in park, and scoot way across the truck and roll up that window. So, when I do the power windows as described in the "power windows on the cheap" thread, I will want to add a controller. I'm not too much into the idea of mounting typical power window buttons, I just don't like the look. So, I got a cruise control stalk. They reproduce these now, but I got an old used one off eBay.

Attachment 2151774

Now I am working on the idea of using that button to roll the window up and down, and I've also considered hiding my garage door remote and operate it via a relay, and perhaps temporarily turning on windshield wipers (mist control), and perhaps one day in the future install cruise control. Do all those things and more with one button.

The code:
https://pastebin.com/dPbVhxqk

Demo video of the code:
https://www.youtube.com/watch?v=xDpqLDz1xEk

So what are the best button press patterns to use to do the various things? My initial thoughts are the cruise control pass through as described in the program is likely to work fine. That is a slow press followed by slow release, and is sent to the cruise control as a fast press followed by finger controlled slow release. Then the next most frequent thing I would do is rolling that passenger window up and down. So I would probably do that with a fast press to start the window moving, and release the button to stop the window rolling. I will program it so every time I operate the window it would move in the opposite direction compared to the previous movement. Quick press and release can do the garage door remote.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Does that cruise control button have two contacts in it? It's got three wires for some reason. Could it be that pressing the button part way does something different than pressing the button all the way? If so, then that might give you more options on how to control multiple things with one button.

Re: Any electronics nerds interested in Arduino/Atmel?
 

Yes, 2 sets of contacts, at different depths of button press. It appears to be most useful to detect how fast you are pressing or releasing the button. I can have the Arduino recognize slow press followed by slow release, or slow press followed by fast release, or fast press followed by slow release, or fast press followed by fast release. Partial press and release is also possible, but a little harder to reliably do with my finger without accidentally hitting the deep contact some of the attempts.

Re: Any electronics nerds interested in Arduino/Atmel?
 

That's nifty