Transistor Selection for Switching Relay Coil-with a little bit of info on my "ARSC"

[rxforspeed]

Hi, Rx

Sorry for NOT having read all your explanations in details ( Difficult for me to read BIG pieces of prose on the screen ...)

BUT

There's one thing I didn't see in all these posts ...

use a RC filter between Relays supply and Pic Supply ... Small R ( 10 - 100 Ohms ) not to drastically reduce PIC voltage and BIG C ( 1000 + µF -Low ESR is best- ).

I don't believe that anybody else has mentioned installing a filter between the PIC and the relays, only isolating the relay coils from the PIC's power supply. I'll have to study that section in "The Art of Electronics" before I connect the relays to the PIC's I/O pins on the 5V relay board(s)...

The only Drawback is to power the possible Leds from the relay side of the RC Filter ( inverted logic, then ) ... not too difficult, in fact; and also use an external ref. for ADCs.

I'm sure you meant LEADS here, right? That does bring to mind another idea I had-connecting LEDs to the PICs' I/O pins that will power the relay coils. I've found some schematics using 5V relays and NPN transistors that also incorporate an LED per relay coil into the design. I'm sure I can just follow those if I decide to use the LEDs; that'll just be a simple visual indication of the relay's correct operation (they'll only be on for about 100msec at a time, anyway)...

For ULN 2x0x ... keep in mind those are Darlingtons outputs ... so Vce sat ~1 v ... 5v - 1v = not so much for 5v relays ...

I've studied the datasheets on both the arrays I've ordered, and I believe I'll only use those for the 12V PCB-mounted relays that Melanie had suggested. I'll either use a MOSFET or an NPN transistor to switch the 5V relays on the other board(s)...

Now ... for the Ice Cap ... nothing keeps you away from using a switching regulator like LM 2575 ... instead of a linear low drop '2940.

I'm not familiar with the '2575, but I'll download the datasheet and compare it to the other regulators I've thought about using. Remember, I don't yet have the education you do-I'll only be starting my "higher education" this coming Spring semester (so you can rightfully still consider me a "noob")...

In the end ... do not forget to play the S.Gainsbourg 's tune "Melody Nelson" ... more than perfect for THE Phantom atmosphere.

Alain

A "Phantom of the Opera" melody? I can't claim to be familair with that tune-my musical background has been limited to songs that I've learned to play on guitar, attempted to learn, or wanted to learn, and most of those were Rock/Classic Rock/Hard Rock/Metal (not the horrible death-crap, but good music like Zakk Wylde's BLS). Classical music is rather relaxing, but I wouldn't be able to differentiate between Mozart and Beethoven (sp?) if I had to. I'm sure the owner of the "Phantom", an elderly man in his seventies, would probably recognize the tune...

BTW-Sorry for the "long-winded" post, this really is an attempt to stick to the facts and details without going to far overboard...

Hi Adam,

2N3904, 2N4401, 2N2222, PN2222 are suitable to actuate a small relay.

Thanks for the schematic! I've seen a similar schematic used with Holtek's HT12D decoder IC, but even that datasheet didn't tell me whether a "high" or "low" CMOS level was output from the IC to the transistor...

Transistors of the same number almost always have similar pin placements, not always!

I've got datasheets for most of the transistors I have on-hand, but I'm sure some manufacturers don't follow an "industry standard". I had played around with a few different cheaper transistors from a different manufacturer (unknown) than I had the datasheet for, and the pin-out obviously wasn't the same. No more cheap transistors for me, I'll pay extra to know that the pin-outs on the datasheets I have are correct...

The best way to tell the type of transistor, is the transistor number. The best way to tell the “pin-out” is the data sheet.

What I had meant by the "off-brand" transistors was a cheap $4 order from e-bay for about 700pcs of two different kinds of transistors, 2N3905 PNPs and 2N3563 NPNs; neither of them have ANY markings whatsoever. They came in seperate and labeled bags, but that's one of the main reasons why I need the transistor "tester". No manufacturer name, markings, anything-just a plain black T0-92 package...

True, plain old 2N7000 MOSFET, or plain old BS170 MOSFET is a good choice if you have them on hand.

I've got a few 2N7000's (T0-92) on-hand. I figured I did after I checked the "My Datasheets" section of "My Documents" (under the N-Channel FET folder) and found the datasheet for it. The schematics you posted will definately help me out with the 5V relay board-thanks a lot!

The ULN2004 is a real space saver for multiple relays.
-Adam-

There's currently only four relays on-board this prototype, but I'm sure I'll have one or two others down the road with eight or more relays to control not only the "fill" valves to compensate for minor leaks over time and keep a single preset ride height/psi level, but for multiple and possibly user-adjustable ride height/psi level settings that will operate all four "fill" valves and all four "dump" valves per vehicle...

GLCD commands would come in handy here for a custom gauge display, and possible touch panel controls...but there's already a digital psi gauge in the "Phantom", I just need to control the air in the 'bags for this application.

Thanks again for all the help and cooperation with this, I really have gained a better understanding (of at least one application) of where and how to use transistors and transistor arrays and a good basis for using relays with PICs. All your input and suggestions are greatly appreciated!

Sincerely,
-Adam Collins