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Forum Index : Microcontroller and PC projects : How many UBW32 CMM’s are out there?
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TassyJim Guru  Joined: 07/08/2011 Location: AustraliaPosts: 6099 |
The forward voltage drop of a LED can be anywhere from 1.6 to 4 V depending on colour and style. This makes getting the resistor value correct, especially when running of a 3.3V supply, difficult without individual measurements. Jim VK7JH MMedit MMBasic Help |
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bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Ok this has got my A$$ moving and I tested it.. This is the results I found LOW level from PIC output is 0.64V (my calc used 0v) Voltage drop across 47 Ohm is 0.75v Voltage drop across LED is 1.92V 3v3 Rail is at 3.31V From the above the calculated current is (0.75/47) = 16mA (acceptable but still a little high) As to TassyJim, Yes there are many different forward Voltages.. Any that are above 3.3v will probably not light at all in this circumstance as it is a 3.3v supply... Blue LEDs are often around 4v.. I generally use 2.1V as my `average LED Fwd V, but as you say you really need to know LED you are using to be accurate.. As it turns out LEDs are quite forgiving and work from as low as 1mA and as high as 50mA. The problem we were looking at was excessive load on the PIC pin but as the LOW level is at .67V (rather high I am surprised at that) it would bring the current well within spec of the PIC anyway. With the change I made to 120 Ohm the current (in my circumstance) would end up as 6ma which I am happy with as well (I prefer between 5ma and 10ma) Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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| arvindk Newbie  Joined: 31/10/2011 Location: AustraliaPosts: 10 |
Hi Mick First of all thanks for a great PCB. I have just finished building it and almost everything works well. Why the almost ? here goes:- I loaded the CAN version just because it is there 
I found two CAN chips - one ending with suffix -I and the other -E, I have the datasheet but I am not clever enough to decipher the difference. Whic one do you recommend ? BTW, I know zilch about the CAN bus and protocol and am not likely to use it anytime soon.... but I wonder if somehow the MMBasic with CAN differs in some subtle ways. I have found the following problems, There is nothing in variables mm.Date$ and mm.Time$. I have the DS1307 installed (brand new chip) the 5 and 3.3 voltages are correct but after setting the variables, there is no incrementing of the variables. They only return values as entered. Is it my wiring fault. or is there something I overlooked ? The autorun.bas file loads but the teraterm shows only the standard header at startup. If I just hit enter at the > prompt. it seems to run, the prompt changes to the option as set in the file but a second line which says- Print "Welcome String" - never executes. I also cannot work out how to save that file to the internal A: drve. In the end may I express some minor regrets :- In the interest of keeping the board small, there is no room for the backup battery, and the PWM connector socket cannot fit because the 26-pin GPIO and the VGA connector squeeze it in. I just soldered fly-leads. Finally, JP3 seems to for programming, with PGd and PGC going to it, but why does pin 3 have A14 coonected to it? Again. I just used flylead to 5 pins at the top edge of the UBW32 to connect to the PICKIT3 for flashing the firmware+ bootloader as suggested by you. Could I have not set something in the config bits which may be causing my issues? Whew, that IS a handful, but hope you can help and set me right. Thanks |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6099 |
Try Date$ and Time$ without the mm. Jim VK7JH MMedit MMBasic Help |
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| bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2914 |
Hi Ardvindk, I am on holiday at Mildura at the moment and not in a position to answer all just now as I have no MM with me (I know... sacrilege...) If no one else helps you between now and when I get back on the weekend I will try to answer your questions. I will say ... YES the PWM header is tight but it does squeeze in but need a bit of force... maybe shave a bit off the 3 pin header to make it easier to squeeze in.. Ahaa but I use just a 3 pin header not one that is with a locking tab.. Yes it IS very tight. The battery I recommended DOES fit ok under the UBW but I had to extend the wires to get to the header which is not under the UBW (maybe I should have put the header under the UBW too but then an external battery pack would have needed the UBW removed to fit. I cant comment on CAN now but I stole the circuit from the DM series and I am told that it does work but you need the correct version (a special at this time I believe) to use it.. The -E version is just an extended temperature range and can be interchaged fpor the -I as far as I believe. I have always set the date by doing DATE$="27-03-13" for todays date Time$="16:58" then Print time$ Print date$ to save to internal A: save"a:test.bas" files"a:" to display A: directory JP2 and JP3 are not programming headers but are link options to select either ISP or i2C (I think from memory) onto the ARduino header (in this case GPIOb) the same as in Geoffs original circuit for the CMM In finishing I looked firstly for a CHEAP, NEAT and SMALL case and then designed the PCB to fit.. I would have liked it about 5mm wider and longer but I couldnt fit my requirement for the 3 categories (CHEAP, NEAT and SMALL). And I really just squeezed it all in. Thanks for your comments and I will try more detail when I am home and can see what we are on about. Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
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