Post by thread:OT: PIC power supply

> This summer I'm going to be working on a project with a multi-drop > network of PICs connected to a Linux box. The network cable will > be about 75 long. Some of the devices will be out in a garden shed and > I would like to power them off a Ni-Cad battery/Solar battery > combination > I'm wondering if a switcher setup would be more effecient (I'm worried > about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )? Why not power the nodes over the cable? I'd use RS-485 over two-pair cable, and use the second pair for 12V DC power. Saves a lot of messing about with batteries and solar cells. Cheers, Eric

On Mon, 16 Feb 1998 13:32:39 -0500 Undetermined origin c/o LISTSERV administrator <.....owner-LISTSERVKILLspam@spam@MITVMA.MIT.EDU> writes: >This summer I'm going to be working on a project with a multi-drop >network of PICs connected to a Linux box. The network cable will >be about 75 long. Since you're going to wire all the PIC boxes together to a central unit that has mains power, run power over the wires. Supply about 12V and use local regulators (78L05) at each PIC so the voltage drop in the wiring isn't a problem. If the PICs have to keep running when utility power fails, a central backup battery could be used. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

Eric Smith wrote: > > > This summer I'm going to be working on a project with a multi-drop > > network of PICs connected to a Linux box. The network cable will > > be about 75 long. Some of the devices will be out in a garden shed and > > I would like to power them off a Ni-Cad battery/Solar battery > > combination > > I'm wondering if a switcher setup would be more effecient (I'm worried > > about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )? > > Why not power the nodes over the cable? I'd use RS-485 over two-pair > cable, and use the second pair for 12V DC power. Saves a lot of messing about > with batteries and solar cells. For one this I won't learn nothing if I keep taking the easy way out ;-} Actually I've am going to do this for the initial setup. But I also want to experiment, I want to keep up those talents I learned in school. My job is in the network field and has nothing to do with my electronics degree. A solar panel will also quench my curiosity about solar power and batteries. I have plans to build all sorts of weird projects some are just mechanical and the PICs and electronics are just used for measurements. -- Neil Cherry http://home.att.net/~ncherry ncherryKILLspamworldnet.att.net "Don't kill him, if he's dead he won't learn nothing" Joker (Batman II)

You could even power the system over a single pair. 1. Analog data from a typical modem IC can co-exist on a DC power feed. 2. If speed is not a problem (which it almost certainly isn't here) you could use DC signaling on the pair AND draw power off when the data signal is high. Example: This is harder to explain than to do!. I'll have to get an automated Protel to ASCII converter :-)) Power is fed from an eg 12 volt supply. Line resistance is low over this distance - say 10 ohms. Minimum acceptable voltage on line due to loading is, say, 7 volts allowing 2 volts headroom for a regulator at each station. Allowable drop is therefore (12-7) = 5 volts. If the 10 ohms was the ONLY resistance then you could draw 5v/10r = 0.5amp. So, place a, say, 20 ohm resistor in series with the power supply. Total R is now 30 ohm max. If you short the line at any point you get a maximum of 12/20 = 0.6amp and minimum of 12/(20+10)=0.4 amp. Each PIC station has: A voltage regulator. A transistor which can short the line. The ability to sense line voltage. If there are 10 stations drawing 10ma each you have 100ma continuous drain. Assume it is all at the far end of the line (worst case). The idle voltage is then V = 12 - (0.1 x (10+20))= 9 volts. If ANY PIC wants to transmit it shorts the line with its transistor and ALL other stations see the line voltage drop to a low value = logic 0. Power feed also stops during this "logic low" condition. Each PIC needs enough reservoir capacitor to hold up during the worst case string of logic lows. Suitable design can ensure that the line is always "high" long enough to keep stations alive. This system is wasteful of power (in this example 12x12/20 = 7 watts is dissipated in the 20 ohm feed resistor when the closest station is transmitting) but the power can be tailored to "just work" in your case and the feed station can probably be mains powered. This sort of system will work effortlessly at low baud rates (1200 baud) and can probably be made to work at much higher ones. The stations can be very low cost (PIC, regulator (possibly only a zener), small TO92 transistor (minimal dissipation off or on)) National Semiconductor once suggested something like this with their now ancient 14469 AART transceiver IC. The application notes may still be available somewhere. . DIAGRAM: Consumer Warning The following diagram made sense in WordPad in Windows 95 using Courier font. When copied to IE4 email it makes none. Depending on your browser YMMV. V+ ---- | R R <-- This R allows supply to be shorted for signalling. R | | <-- Data and Power line --> ___________________________________________________-> more PICS | | | __________ ____________ |C | | | | | |/ ----- | Regulator|---| PIC |--RRRR--| |__________| | | ___________| b|\ | C | |E | C | | _______________|______|_______|_________________|___________ ___ PIC will also need to sense line voltage (not shown) C is essential to keep PIC powered during data low {Original Message removed}

Undetermined origin c/o LISTSERV administrator wrote: {Quote hidden}> Eric Smith wrote: > > > > > This summer I'm going to be working on a project with a multi-drop > > > network of PICs connected to a Linux box. The network cable will > > > be about 75 long. Some of the devices will be out in a garden shed and > > > I would like to power them off a Ni-Cad battery/Solar battery > > > combination > > > I'm wondering if a switcher setup would be more effecient (I'm worried > > > about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )? > > > > Why not power the nodes over the cable? I'd use RS-485 over two-pair > > cable, and use the second pair for 12V DC power. Saves a lot of messing about > > with batteries and solar cells. > > For one this I won't learn nothing if I keep taking the easy way out ;-} > > Actually I've am going to do this for the initial setup. But I also want > to > experiment, I want to keep up those talents I learned in school. My job > is > in the network field and has nothing to do with my electronics degree. A > solar panel will also quench my curiosity about solar power and > batteries. > I have plans to build all sorts of weird projects some are just > mechanical > and the PICs and electronics are just used for measurements. > > -- > Neil Cherry http://home.att.net/~ncherry .....ncherryKILLspam.....worldnet.att.net > > "Don't kill him, if he's dead he won't learn nothing" Joker (Batman II) The Cherry Semiconductor CS212 security chip runs on an extremely easy one-wire protocol that also powers the nodes. It is made for long runs like you describe. You could probably hack the protocol to work for your PIC nodes. You can look in a Maplin catalogue (catalog), or you can look on the Cherry site. There is a link on this page : http://www.wasp.co.za/~tjaart/electroniclinks.html BTW : Your name reminded me of the chip! -- Friendly Regards Tjaart van der Walt EraseMEtjaartspam_OUTTakeThisOuTwasp.co.za _____________________________________________________________ | WASP International http://www.wasp.co.za/~tjaart/index.html | | R&D Engineer : GSM peripheral services development | | Vehicle tracking | Telemetry systems | GSM data transfer | | Voice : +27-(0)11-622-8686 | Fax : +27-(0)11-622-8973 | | WGS-84 : 26¡10.52'S 28¡06.19'E | |_____________________________________________________________|

Neil, I'm working on a water pond with a waterfall. I want the pump to run off of batteries charged by 12VDC as well as a solar panel. I have decided on sealed lead-acid batteries. While this is still very preliminary, I'll be using a PIC for control. I'm sure I'll have a lot of questions about PWM control later this spring. I'll be glad to share my work. - Tom At 01:32 PM 2/16/98 -0500, you wrote: {Quote hidden}>This summer I'm going to be working on a project with a multi-drop >network of PICs connected to a Linux box. The network cable will >be about 75 long. Some of the devices will be out in a garden shed and >I would like to power them off a Ni-Cad battery/Solar battery >combination >I'm wondering if a switcher setup would be more effecient (I'm worried >about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )? > >I'm also looking for easy to find parts (1sy-2sy) and this is a hobby >project. > >Thank you. > >-- >Neil Cherry http://home.att.net/~ncherry ncherryspam_OUTworldnet.att.net > >