tag:blogger.com,1999:blog-5485549003242897389.post1250034983358649485..comments2024-02-20T02:58:19.459+01:00Comments on Tom's Projects: Musings on CharlieplexingTom F.http://www.blogger.com/profile/17222198163820671255noreply@blogger.comBlogger31125tag:blogger.com,1999:blog-5485549003242897389.post-79326268856539075422016-06-05T17:58:07.482+02:002016-06-05T17:58:07.482+02:00This comment has been removed by a blog administrator.michellehttps://www.blogger.com/profile/17062537165147135952noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-80163053938597634962013-09-08T10:51:30.690+02:002013-09-08T10:51:30.690+02:00Thank you!
And yes you are right, R1-R5 are usele...Thank you!<br /><br />And yes you are right, R1-R5 are useless. I put them in out of caution. This was an experimental set-up and I wanted to add some protection against short circuits, etc.Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-2229760721481195342013-09-08T05:42:16.302+02:002013-09-08T05:42:16.302+02:00This page is the best explnataion of how to do cha...This page is the best explnataion of how to do charlieplexing properly that I have found.<br /><br />What's the purpose of R1-R5, in my experience emitter followers self-limit the base current.<br />Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-67768631481896768912013-08-22T22:09:37.261+02:002013-08-22T22:09:37.261+02:00Alexander, I don't think that those resistors ...Alexander, I don't think that those resistors help discharging any capacitor. But I don't really understand what you mean by delay. The multiplexing happens at high speed (>100Hz), so a switching delay should not be visible. Could there be a problem with your software?<br /><br />Yes, the wikipedia example shows that there are alternative current paths. This is really a problem, when Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-49088743598391290932013-08-21T11:02:14.785+02:002013-08-21T11:02:14.785+02:00I made a matrix using your design but omitting the...I made a matrix using your design but omitting the base resistors and it seems there are capacitance problems with the transistors delaying when I switch them off. Maybe the resistors in your circuit help to discharge the capacitance ?<br /><br />Btw the problem with the wikipedia example is that when you set a pin as high , another as low and the others as high impedance , there are more than Alexanderhttps://www.blogger.com/profile/06290020248171490541noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-36890255302522254692013-08-20T22:37:29.256+02:002013-08-20T22:37:29.256+02:00PS: It might actually be possible to omit the 270 ...PS: It might actually be possible to omit the 270 Ohm resistors as well, depending on your supply voltage. The controller's IO pins can only drive a certain amount of current and that current will be not enough to destroy the LEDs.<br /><br />What happens is that a heavily loaded IO pin will not be able to "deliver" a "clean" low. Instead, the voltage will be somewhat Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-10864494301073389732013-08-20T22:28:01.388+02:002013-08-20T22:28:01.388+02:00Alexander, I think you can omit those resistors wi...Alexander, I think you can omit those resistors without any consequences.They can be useful if you are experimenting and something goes wrong (like a short circuit).<br /><br />I added them to limit the transistor's base current. But under normal circumstances, higher base current means higher LED current, which means higher LED voltage, which means lower base-emitter voltage, which means Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-55564765288660909752013-08-20T21:55:09.967+02:002013-08-20T21:55:09.967+02:00Alexander, the answer is obviously, that an LED ca...Alexander, the answer is obviously, that an LED can't light up without the cathode low and the anode high.<br /><br />In principle, charlieplexing is implemented just like in the Wikipedia. The only difference is that I added driver transistors to the anodes of all LEDs.<br /><br />The transistors behave like non-inverting drivers.<br /><br />Keep in mind that in my matrix, exactly one Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-60133125946539366782013-08-20T18:05:20.154+02:002013-08-20T18:05:20.154+02:00Tom here is another question. Are the base resisto...Tom here is another question. Are the base resistors required and how would it affect the circuit if we omitted them ?Alexanderhttps://www.blogger.com/profile/06290020248171490541noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-22311318922937442712013-08-13T00:12:08.121+02:002013-08-13T00:12:08.121+02:00How can a led light up without having it's cat...How can a led light up without having it's cathode Low and it's anode High? I can see how it would affect things in the wiki example but we are implementing charlieplexing differently here.Alexanderhttps://www.blogger.com/profile/06290020248171490541noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-20896290979978693112013-08-06T18:19:16.963+02:002013-08-06T18:19:16.963+02:00Yes, they would. This is a limitation of charliepl...Yes, they would. This is a limitation of charlieplexing.<br /><br />Wikipedia says (http://en.wikipedia.org/wiki/Charlieplexing):<br />Forward voltage<br /><br />When using LEDs with different forward voltages, such as when using different color LEDs, some LEDs can light when not desired.<br /><br />In the diagram above it can be seen that if LED 6 has a 4v forward voltage, and LEDs 1 and 3 have Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-35646245408365258342013-07-31T14:59:37.652+02:002013-07-31T14:59:37.652+02:00Hey Tom, wouldn't wiring rgb leds like this cr...Hey Tom, wouldn't wiring rgb leds like this create problems because of the different voltage drops?Alexanderhttps://www.blogger.com/profile/06290020248171490541noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-80306936451933774142013-07-14T02:15:36.944+02:002013-07-14T02:15:36.944+02:00Alexander, the collectors all go to +5V, that is w...Alexander, the collectors all go to +5V, that is what the little arrows symbolise.<br /><br />Don't worry too much about the 100n capacitor. It is a decoupling capacitor.<br /><br />http://en.wikipedia.org/wiki/Decoupling_capacitor<br /><br />It is there for moments, when the circuit needs a lot of current in very little time. It then acts as a kind of high speed battery. <br /><br />It mightTom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-70992483236345059972013-07-10T13:36:36.437+02:002013-07-10T13:36:36.437+02:00Dear Tom,
I have to say I am new in electronics a...Dear Tom,<br /><br />I have to say I am new in electronics and can't read schematics properly. So where exactly do the collectors of the transistors go to and what's the role of the 100n in the circuit? Thanks in advance!Alexanderhttps://www.blogger.com/profile/06290020248171490541noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-56347965867898328282013-05-19T22:18:54.416+02:002013-05-19T22:18:54.416+02:00Dear Tom,
Thank you for the answer. Now I underst...Dear Tom,<br /><br />Thank you for the answer. Now I understand your circuit very well. You are using all in the LED's in forward bias mode i.e, they are powered by the transistors. <br /><br />As per the microchip appnote and this link : http://www.josepino.com/microcontroller/how_control_leds :- the difference in connecting leds one in forward bias and other in reverse bias to the same portMukhthar Ahmedhttps://www.blogger.com/profile/06932521916081677055noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-61915021624120593922013-05-19T19:20:21.620+02:002013-05-19T19:20:21.620+02:00Ahmed,
yes, this is a very important point I was ...Ahmed,<br /><br />yes, this is a very important point I was trying to make in this post. Most people maintain that with charlieplexing, the duty cycle is 1/(number of LEDs). They say that because they assume that only one LED can be active at any time.<br /><br />But this need not be true. In my smaller 3-port example (with the driver transistors), there will be one port "high" (Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-57113523362647666972013-05-15T22:31:51.345+02:002013-05-15T22:31:51.345+02:00Hello,
Could show explain how you calculate the d...Hello,<br /><br />Could show explain how you calculate the duty cycle in multiplexing?<br /><br />20 LEDs 5 ports at a frame rate of 50Hz : this means u scan the entire 20 leds at 50hz<br />4 LEDs simultaneous update rate 250Hz : this is 5 times more<br /> in your blog : The duty cycle for a 6 LED set-up is again 33% :- how did u arrive at 33% duty cycle?<br /><br />This same comment is on Mukhthar Ahmedhttps://www.blogger.com/profile/06932521916081677055noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-84644752384532769872013-04-25T22:26:37.418+02:002013-04-25T22:26:37.418+02:00Hi p3lb0x, thanks for letting me know. I had a loo...Hi p3lb0x, thanks for letting me know. I had a look at your video and it really looks great. The 7x8 matrix is quite impressive.Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-84888209393850103802013-04-25T18:31:21.001+02:002013-04-25T18:31:21.001+02:00Hi Tom. I just wanted to say thanks for this post....Hi Tom. I just wanted to say thanks for this post. You helped me immensely with a school project involving Charlieplexing. I based a lot of my initial design on your LED matrix-like circuit diagram.<br /><br />In case you want to check out what I made, check this youtube link.<br />http://www.youtube.com/watch?v=7IZT2XLVnX0p3lb0xhttps://www.blogger.com/profile/04295015834602719637noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-39919402579568140792013-03-15T20:13:41.359+01:002013-03-15T20:13:41.359+01:00Hi,
i used the AVR Studio, available free of charg...Hi,<br />i used the AVR Studio, available free of charge from Atmel. You start a new project, point it to the right directory and to the downloaded asm file.Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-75822732123074013822013-03-15T15:18:00.447+01:002013-03-15T15:18:00.447+01:00hi tom..
just want to know what compiler did you ...hi tom..<br /><br />just want to know what compiler did you use for the program? tnxAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-39623700218299082222011-10-27T21:02:40.417+02:002011-10-27T21:02:40.417+02:00Ah, you are partly right. But consider how the mul...Ah, you are partly right. But consider how the multiplexing works. The transistor supplies a full column of LEDs. The cathodes of the LEDs of that column are connected to one port each. The uC ports can source/sink enough current for one LED. So there is no need for a transistor on the rows. But for the columns a transistor _is_ needed.Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-57430436391711045752011-10-27T18:21:10.196+02:002011-10-27T18:21:10.196+02:00I have a question...
The transistors are used to s...I have a question...<br />The transistors are used to source a higher current than what your uC can handle, right? But this current is sunk through the uC pins anyway. Therefore the transistors are useless?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-52841486757338281852011-09-22T05:33:53.503+02:002011-09-22T05:33:53.503+02:00Thanks for the response - I am going to try your 4...Thanks for the response - I am going to try your 4x4x4 cube. I'll let you know how it goes :)Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5485549003242897389.post-70600941580804909302011-09-21T22:52:42.208+02:002011-09-21T22:52:42.208+02:00Exactly. I didn't have the right values for th...Exactly. I didn't have the right values for the resistors, so I used them actually in parallel.Tom F.https://www.blogger.com/profile/17222198163820671255noreply@blogger.com