transistor switch help

i thought of doing the following

so replace R2 with 430R so Q1 can sink a little more and adding a 1K to Led, would this work? (nowhere near ready to sim stuff on spice yet lol or i would try it on that

Your new circuit with the LED will work fine.

Little Ghostman said:

(nowhere near ready to sim stuff on spice yet lol or i would try it on that

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What then you won't have any magic smoke

audioguru said:

Your new circuit with the LED will work fine.

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I couldn't think of anywhere he could put the LED, everywhere I tried and failed. When he dropped into the collector, I thought that will work, that will work.

I'm glad I'm not designing it or there would be magic smoke

Good Job, LG. We want details

i have added a sense resistor but would like to add a indicator LED, i have thought about it but not sure the best place to place it, i would like to keep the mA from the pic pin down as much as i can, the LED need only be run at around 10mA so where would be best in the circuit with the least inpact??

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Hi L,
Add a series resistor and LED across the Inductor, ie: in parallel with the inductor.
Set the LED current at say 15mA, if the led is Red with a Vforward of say 2Volts, that would make the resistor value >
[12V-2V]/0.015 = 666R, use a preferred value of 620R or 680R

How do you plan to use the voltage across the sense resistor.?

E

EDIT:
With the LED in the position shown in your posted circuit, all it will tell you, is that Q1 is working.
It will give no indication if Q2 and the Inductor path is working as expected.

hi Logan,
If you have installed LTSpice you could try running this 'asc' simulation.
I have used a 2N2907 in place of the MPSA because its included in the LTS transistor select option window.

Note the very low Vsense of ~15mV, this why I asked how you are going to use it.?

E

hi back from school! will update later as home work needs doing also will give me time to think. thank you for sim i will load it and take a look . Also dad has agreed not to look in this thread and i did point out that as a mod you can see which threads he peeks in , so will give further details of master plan later lol
LG

tried to run the sim and got the following error


Circuit: * C:\Users\jason\AppData\Local\Temp\Logan52a.asc

Error on line 2 : q1 n005 n007 0 0 bc547a
Unable to find definition of model "bc547a"
Error on line 10 : d1 vsense n003 1n4001
Unable to find definition of model "1n4001"
Error on line 13 : d2 n004 0 dled_rd
Unable to find definition of model "dled_rd"
Direct Newton iteration for .op point succeeded.

Date: Tue Nov 12 15:48:12 2013
Total elapsed time: 5.220 seconds.

tnom = 27
temp = 27
method = modified trap
totiter = 9468
traniter = 9450
tranpoints = 4589
accept = 3558
rejected = 1031
matrix size = 13
fillins = 0
solver = Normal
Matrix Compiler1: 674 bytes object code size 0.6/0.2/[0.2]
Matrix Compiler2: 80 opcodes 0.3/[0.1]/0.2

hi L.
You must place the asc files in the LTSpice folder, mine is C:\Program Files\LTC\LTspiceIV
That folder is created when you install LTSpice.

I then create my own sub folder to LTspice, called MyWork: C:\Program Files\LTC\LTspiceIV\MyWork\Logan52a.asc

Move the asc file and retry the sim.
E

LT Spice does not know about a European BC547A transistor and a 1N4001 rectifier diode. Those models must be found at the Yahoo Group.

hmm i should have realized that the sense resistor would be low at only 140 mA being drawn by the fan. due to low time before i need to actually build the sense resistor will stay, i was going to connect to the pic ADC but for now any unused pic pins will be brought out to a header on the board in case i need to add something later. This whole thing may seem mad but it's about alot of things including a chance to try many things out and learn alot.
i will be using 3 pic boards for the fans to start with, one for each zone, with 3 fans per board. one reason is the code as well, it's easier at this point for me to break stuff down to small numbers instead of trying to get 1 pic to do everything. The boards will be talking to each other over SPI. please dont think i dont know i am over engineering and using more stuff than needed, i am using what is here and it's a fantastic chance to learn. At some point i might add a op amp to the sense resistor so i get a chance to use and learn about them. the boards will all be small and the pics in sockets so if i run them for a few days and want to add something but need to make a new board up that isnt a bad thing, i can desolder what i need to keep like sockets and pics or chips and make a new board up, the way i see it i have 15 large pcb boards that i can probably cut up to get 60 boards out of. If needed i can use it all up and gain alot of experience in home rolling pcb's!

i am also going to use ntc thermistors for the fans (inside incubator 3 per region to monitor heat in zones and control fan speed dependent on heat distribution) LM sensors on another board in conjunction with ds18s20's for controlling the actual heaters. also once my incubator is running (needs eggs in soon as poss) i will do a board or add to a board humidity control. then after i have experimented and got a good idea of what is working and what is not i will start to develop one or two boards with all the best bits on of these dev boards i am doing so eventually i will only have 1 or 2 boards!
ok its not how its done in industry etc but this is as much about learning and having fun than just trying to get a working solution!

as for the info on setting up the folders for LT spice i will do that and let you know how it goes. if i put the diode as you suggest will it affect the running speed or voltage going to the actual fan in anyway?
if not then i may keep both Led's also i might do away with the inductor LED if i go the sense resistor route with or without op amp.
i am not having to buy much in except a couple of cheap heating elements ment for hair straighteners!!
all this other stuff is already here.
also at some pont i would like to try a couple of different ways to data log, i have found some obsolete Sram and fram chips here and a couple of the sim card type things so another chance to learn!!
over engineered YES! over the top feature creep! YES definitely but thats the way i would like to learn and i dont mind doing the work and trying to come up with the solution;s then just asking you guy's if i am doing it correctly and getting you to look over my assumptions and workings out, please dont think i am asking anyone to design it for me because that isnt the intention, but i do and will continue to take on board all your advice. BBL
and many many thanks for all the help so far i have learnt more in last few days than i have in months of reading up!

LG

Thank you AG dad joined so i will go get them from the group, i couldnt join as they need a cell number in yahoo groups and i am only allowed a cell phone to call mum and dad if i miss school bus or something and need there help, i am not allowed to give the number out

i tried uncle eric but looks like i need to download the models as the sim opens ok but cant find parts, so will go download them from user group

i cant find them yet at the group but LT does have another bc547B so might use that, but want to crack adding libs to spice so will keep looking when i get back from school later

Little Ghostman said:

i cant find them yet at the group but LT does have another bc547B so might use that, but want to crack adding libs to spice so will keep looking when i get back from school later

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hi L,
What I could do, is post some of my lib/sub files for you.?
E

that would be great thank you, i have tried downloading some files but not had success yet in getting them to work! i will do some reading upon adding files to spice, i have a question on the circuit but i want a crack at answering it myself if i can get spice sorted out

The BC547A is used as a simple saturated switch so a BC547B or BC547C will work exactly the same with a base current of 1/10th or 1/20th the collector current.

A BC547A has fairly low current gain, a BC547B has normal current gain and a BC547C has high current gain.
But current gain is used for a linear amplifier, not for a saturated switch.

hi all, ok ive got LT spice sorted! (thanks eric for files), going to go with both LEDS for now, idea is build this quick as poss and get eggs in, then i can modify my design as i go along. This version V1 will be pretty basic just to save time but i can swap out the boards as i go.
will look at adding opamp for V2, i also need to get the heater board sorted, that will use ds18s20 and probably some kind of burst mode heating, the fan board also needs the LM temp sensors or maybe NTC thermistor because each of the 3 fans in a zone will be speed controlled depending on the temp in that part of the zone, (it makes the incubator have a really even temperature and worked really well with dads old commercial incubators he built for the farm), dosnt need DS18s20's for that, as long as each zone has 1 DS in the center that helps control the main heater then the fans that even it all out dont need anything more than thermistor or the LM, not sure if i can find any LM's here at the moment so might have to use thermistors as i can lay my hands on some 10K ones (they have been unpacked lol).
part of the code has been done for main heater board but needs a tweak, also going down the max232 route so i can get datalogging going, that will be each chip talking over spi to a master and from master to max232 to pc. Also in later version will add in the card thing or something like that .
i have ordered a seconhand book about transistors off of ebay, was only £1 and i like reading books.
going to see if i can ind what op amps we have kicking about in easy reach and have a go in spice to see if i can work out a circuit to up the sense resistor output, i am thinking something like 1000-1 gain then into pic ADC, so normal running will give me around 1.5V (each fan) on the op amp output.
really looking forward to op amps.
Alo looking at the humidity control stuff and i have a great idea or controlling the humidity so will post details in a day or so.
thanks again everyone i am learning loads from you all and i am enjoying this project!

thanks AG for info, i have a speaker (8 ohm pc speaker) that i am going to use for simple alarm sounds etc for over temp and such, so i might get a chance to use transistors as a simple amplifier! nothing fancy but a good chance to have a go and learn a bit more

p.s i have also joined a maths group to try and get my maths upto scratch as i am rubbish at it!

i have done most the woodwork now, i am doing a updated schematic for each zone fan controller but have a small problem, normally i go the 40 pin chip route for testing and prototypes then i down grade the chip once i know exactly what i want it to do and how many pins etc i actually need. this time i was going to go straight for a smaller pic, so i went to have a look what small pics we got and i have 4 18f1330's great 18 pins blah blah blah, but it dosnt have spi, it does however have 3 pwm generators with 6 outputs, wich would save me coding interrupt driven pwm.
one way i can think of making it easier for me is to use the 1830's as fan drivers and connect the EUSART (it has one) to a master pic with 2 usarts one for connection to pc and one to connect to the fan controller chips. not sure on all this so will try it, i will make a single board first to control 3 fans, if it works out ok i will do a bigger one with all three pics for the fans on. so today is finish schematic for test board and with luck have time to make test board. or find bigger pic and go the 4 fan per zone route with software pwm, lets try the 18f1330 first. will post schematic later
logan

edit

forgot to add i have been playing with dads super duper function generator to find best frequency and duty cycles for the fans, will post results and pics later. I am ment to use opto isolator with his FG but could only find a triac one so didnt bother
the fact he wants me to use a opto makes me think he paid more than the £20 for it that he told mum it cost

here is the first fan driver board revised schematic

not as tidy as i like but was a slight rush job, the inputs and outputs maybe swapped over to D type sockets on the project box but for the sake of pcb layout i have used T Blocks. The Led's will be panel mounted. wich reminds me i havnt added 12V power indicator i will go do that now! then do the pcb layout