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| Thread ID: 60788 | 2005-08-13 03:31:00 | Transistor Driver | Dannz (1668) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 380670 | 2005-08-13 03:31:00 | I have an astable multivibrator which i want to control with my computer I have a program written that turns Data 0 of the LTP port on and off, but the voltage is too low to run the multivibrator. How do i use a transistor to use a 9v battery to power the circuit. Thanks |
Dannz (1668) | ||
| 380671 | 2005-08-13 03:59:00 | HELP!, this is urgent. Any links would also be appreciated |
Dannz (1668) | ||
| 380672 | 2005-08-13 04:04:00 | You can only get a few mA from a printer port pin, so that might be the problem . You should have 5V . Are you sure you are actually using an earth pin . There are quite a few "specified" as earths, but they might not all be connected . ;) I can't remember off hand which are the most likely, but pin 19 comes to mind . Sometimes I use a port powered device and use several data pins as supply . I connect them through a Schottky diode (low forward volts) to stop accidents . The simplest way to connect a switch is with an NPN, but you have to be careful, because it needs to be connected in the "low" side . That is, you connect +9V-->load+, load- --> transistor(collector) and transistor(emitter) --> ground/-9V . Then a 1k or so from the printer port pin to the base will work it . That means that the "ground" of the circuit is not the same as the computer's earth . It will be up by the saturation voltage of the transistor . If you use the NPN to turn a PNP on and off, you can put the PNP in the high side . For that you connect +9V --> 1k-->NPN(collector) and NPN(emitter) --> ground, and again a 1K from the port to the NPN(base) . Also +9V --> PNP(emitter) and PNP(collector) --> load+ and load- --> ground . The PNP(base) is fed from the NPN(collector) . That will give Port High --> NPN on, so it turns the PNP off . Port Low -- NPN off, so the PNP is turned on by the resistor . So you will be using Negative logic, which has an illustrious history . |
Graham L (2) | ||
| 380673 | 2005-08-13 04:15:00 | For Some reason that isnt working - im using 5v for the power (USB Port) | Dannz (1668) | ||
| 380674 | 2005-08-13 04:21:00 | For Some reason that isnt working - im using 5v for the power (USB Port) What isn't working? I often use USB for 5V, that's a good 500 mA. But my laptop gives weird crash patterns on the screen when I short it. :( Are you sure of the pinout of the transistors you are using. Be aware of the difference between looking from the top and loOking from the bottom. ;) I take it you are using something like BC547 for the NPN and BC557 for the PNP? P.S. You need two wires at least from the printer port the data line you are using and an earth. If the earth of your circuit isn't connected to the earth of the computer, no current can flow to turn a transistor on. |
Graham L (2) | ||
| 380675 | 2005-08-13 04:23:00 | Im using BC547 for the NPN and its not turning the multivibrator on | Dannz (1668) | ||
| 380676 | 2005-08-13 04:35:00 | Apart from my P/S . to my previous posting, forget about the multivibrator for the moment . Make the transistor switch first . Assume the emitter is grounded . (Rather, make sure its grounded as far as the computer is concerned), and that the collector has a supply (either through a load or a resistor) . Then if base is high, the transistor should be on . The collector will be low . That means there will be only about 0 . 6V between the collector and the emitter . If the base is low, the transistor will be off . There will be full supply voltage between the collector and emitter . If you're driving from a computer it's quite good to set up a loop so the pin you are using goes up and down at about a one second rate . (I recently did it too fast for the meter I was using to autorange . :( ) |
Graham L (2) | ||
| 380677 | 2005-08-13 04:39:00 | I have a multimeter connected between the collector and +5v and it measures 5v Do you have msn Graham L? it might make this easier |
Dannz (1668) | ||
| 380678 | 2005-08-13 04:50:00 | Nope, and the Library is closing in about 15 minutes . Measure between the collector and emitter to see if the transistor is on . You might "measure" 5V between the collector and supply with a high impedance meter even with the transistor off . Current flowing through the base from a +source to the emitter enables a much larger (by a factor of 100 or more) current to flow between the collector and the emitter in an NPN . In a PNP, a small current flowing from the emitter out through the base to ground enables a much bigger current flow between the emitter and collector . In each case, above a certain flow the voltage between the C and E becomes very low (about 0 . 6V) and the transistor is said to be "saturated . " That's the mdoe wyou want for a switch . |
Graham L (2) | ||
| 380679 | 2005-08-13 04:54:00 | Do you know of a circuit diagram anywhere? | Dannz (1668) | ||
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