Post by thread:[PIC]:Newbie Circuit Question

Hello Everyone, I have a question concerning a circuit I am building. I am building a simple stoplight controller. I have a 9v 500ma wall wart supplying power to a 7805 regulator. The regulator powers the 16f84 Pic. The portb pin is connected to a 1K resistor, that is connected to the base of a darlington transistor. I have a 12.8v 1.04A light bulb connected between the unregulated 9v 500ma supply and the collector of the transistor. The emitter is then connected to ground. The code just sets one pin(portb3)high and the other one low(portb4), and then reverses the process. The problem is the second bulb will not light unless I disconnect the first bulb. Then I reconnect the first bulb and the circuit works fine. Any suggestions for circuit improvement. Obviously I am new to electronics, but I am comfortable with programming. TIA, Kevin PS. I got the circuit off the net. It called for a BD679, but below is the closest I could find. Transistor Specs pwr disp 65w coll-emitr voltage 60v coll-base volt 60v emit-base volt 5.0v coll current continuous 5.0A coll current peak 8.0A base current 120ma -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

"Kevin A. Benedict" wrote: > > Hello Everyone, > I have a question concerning a circuit I am building. I am building a simple > stoplight controller. I have a 9v 500ma wall wart supplying power to a 7805 > regulator. > The regulator powers the 16f84 Pic. The portb pin is connected to a 1K resistor, > that is connected to the base of a darlington transistor. I have a 12.8v 1.04A > light bulb connected between the unregulated 9v 500ma supply and the collector > of the transistor. The emitter is then connected to ground. > The code just sets one pin(portb3)high and the other one low(portb4), and then > reverses the process. The problem is the second bulb will not light unless I > disconnect the first bulb. Then I reconnect the first bulb and the circuit works > fine. Any suggestions for circuit improvement. Obviously I am new to electronics, > but I am comfortable with programming. It sounds like a simple maths problem to me. Wall wart = 500mA 1 light bulb + 1 light bulb = 2.08 Amps 500mA - 2.08A = - 1.580A Well, it doesn't exactly work like that, but you are trying to draw more current from the wall wart than it can supply. Consequently, it's output voltage is dropping down to a point where the regulator fails to work, and also the PIC. Try using a power supply that can supply the required current, or use bulbs that draw less current. Also, if you use LEDs during code development, there is less chance of damaging the circuit and PIC. -- Best regards Tony mICros http://www.bubblesoftonline.com spam_OUTsalesTakeThisOuTpicnpoke.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

Kevin A. Benedict wrote: {Quote hidden}> > Hello Everyone, > I have a question concerning a circuit I am building. I am building a simple > stoplight controller. I have a 9v 500ma wall wart supplying power to a 7805 > regulator. > The regulator powers the 16f84 Pic. The portb pin is connected to a 1K resistor, > that is connected to the base of a darlington transistor. I have a 12.8v 1.04A > light bulb connected between the unregulated 9v 500ma supply and the collector > of the transistor. The emitter is then connected to ground. > The code just sets one pin(portb3)high and the other one low(portb4), and then > reverses the process. The problem is the second bulb will not light unless I > disconnect the first bulb. Then I reconnect the first bulb and the circuit works > fine. Any suggestions for circuit improvement. Obviously I am new to electronics, > but I am comfortable with programming. > > TIA, > Kevin > > PS. I got the circuit off the net. It called for a BD679, but below is the closest > I could find. > Transistor Specs > pwr disp 65w > coll current continuous 5.0A > coll current peak 8.0A > base current 120ma 1. What number is on the transistor? This does not sound like a darlington. 2. You cant run 2x 12v 1A bulbs from a 9v 0.5A wall wart supply. It will not supply enough amps. :o) 3. Can you show the circuit? -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

OK, point taken about the 500ma power supply. >1. What number is on the transistor? This does >not sound like a darlington. I am at work, but does TIP120 sound right. It says darlington on the package. I got it from Radioshack. >2. You cant run 2x 12v 1A bulbs from a 9v 0.5A >wall wart supply. It will not supply enough amps. It is a stoplight configuration, so only ONE bulb is lit at a time loop: BSF RED BCF GREEN DELAY 2 seconds BCF RED BSF Green Delay 2 Seconds goto loop >3. Can you show the circuit? http://www4.tpg.com.au/users/talking/25mA.html It's the fourth circuit down, using the 12c508a The circuit does work if I put a 1.5k resistor for the second bulb. Bulb 1 blinks by itself for two seconds, then it goes into the loop of red then green then red then green ? I realize I should just get the proper 1A power supply! :) Thanks, Kevin -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

kben@dca.net wrote: > I got it from Radioshack. > >2. You cant run 2x 12v 1A bulbs from a 9v 0.5A > >wall wart supply. It will not supply enough amps. > It is a stoplight configuration, so only ONE bulb is lit at a time > loop: > The circuit does work if I put a 1.5k resistor for the second bulb. Bulb 1 blinks > by itself for two seconds, then it goes into the loop of red then green then > red then green ? > I realize I should just get the proper 1A power supply! :) You bet!! Remember too that a 1A bulb will draw a short surge of a LOT more than 1A before the filament heats. Use a big cap across the power rails, probably 2200uF 25v sounds good, more is better. Also, a trick suggestion, allow 0.2 seconds where both bulbs are off before you turn the next bulb on, this will allow a slight break before the next turn on surge. You won't notice this with 2 sec on periods. -Roman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Kevin wrote: >OK, point taken about the 500ma power supply. > > >1. What number is on the transistor? This does > >not sound like a darlington. >I am at work, but does TIP120 sound right. It says darlington on the package. > >I got it from Radioshack. > >2. You cant run 2x 12v 1A bulbs from a 9v 0.5A > >wall wart supply. It will not supply enough amps. >It is a stoplight configuration, so only ONE bulb is lit at a time >loop: >BSF RED Insert at least a couple of NOP's here >BCF GREEN >DELAY 2 seconds >BCF RED And here too. You might be getting bitten by the infamous read-modify-write bug! {Quote hidden}>BSF Green >Delay 2 Seconds >goto loop > > >3. Can you show the circuit? >http://www4.tpg.com.au/users/talking/25mA.html >It's the fourth circuit down, using the 12c508a > >The circuit does work if I put a 1.5k resistor for the second bulb. Bulb 1 >blinks >by itself for two seconds, then it goes into the loop of red then green then >red then green ? >I realize I should just get the proper 1A power supply! :) ___________________________________________ David Duffy Audio Visual Devices P/L U8, 9-11 Trade St, Cleveland 4163 Australia Ph: +61 7 38210362 Fax: +61 7 38210281 New Web: http://www.audiovisualdevices.com.au New email: EraseMEavdspam_OUTTakeThisOuTaudiovisualdevices.com.au ___________________________________________ -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body

>>OK, point taken about the 500ma power supply. The cheap and easy way out, would be to just go buy another wall-wart and run the lights off it separately. That way your lights will be kind of "what you see is what you get" (which is what you were thinking originally), but it won't cause the processor to reset. Tie the grounds (the negative leads) of the two supplies together. For a resetting processor...always ask yourself if what you are seeing would be caused by the program starting over and over again. In your case, yeah. do { turn on the first light; } while(1); -- Barry -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body