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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
 Posted - Jun 08 2011 : 10:20:13 AM
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quote:
Originally posted by codingplanet
I understand bypass caps and lowpass filters (to a lesser degree) and the difference between them. I was not confusing them.
Yes my scope does have those features. And now you have mentioned that, I understand what you were getting at. I can take that measurement sometime this week.
Okay cool. 
I'm happy to help someone out on my breaks.  |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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codingplanet
Mad Scientist
United Kingdom
195 Posts |
Posted - Jun 08 2011 : 10:29:45 AM
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| Aye, thanks a lot for your help :) |
Edited by - codingplanet on Jun 08 2011 10:30:01 AM |
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codingplanet
Mad Scientist
United Kingdom
195 Posts |
Posted - Jun 09 2011 : 3:10:34 PM
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| I seem to have inadvertently killed my device. I will have to debug it some other time. |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Jun 09 2011 : 11:42:26 PM
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quote:
Originally posted by codingplanet
I seem to have inadvertently killed my device. I will have to debug it some other time.
Oops! Shit happens mate. Good luck with your debugging. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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codingplanet
Mad Scientist
United Kingdom
195 Posts |
Posted - Jun 10 2011 : 06:13:01 AM
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| The USB +5v shorted to ground. The USB port is still functional and the PIC is to some extent but I get no USB communication with it. I have a spare PIC I can swap in at some point. |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Jun 10 2011 : 06:43:11 AM
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quote:
Originally posted by codingplanet
The USB +5v shorted to ground. The USB port is still functional and the PIC is to some extent but I get no USB communication with it. I have a spare PIC I can swap in at some point.
Crap! I think all compliant USB ports/chipsets should be current limited to 500mA continuous, so there shouldn't be any damage to the USB chip on your motherboard. Hopefully there's no damage done to your contraption though. Happy problem solving!  |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
Edited by - wasssup1990 on Jun 10 2011 06:44:15 AM |
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paulh
Apprentece
5 Posts |
Posted - Jun 15 2011 : 10:20:05 AM
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| I think this can be really useful as you can see the temperature and voltage on the fly. I have tried a similar project before where in there is an extra bread pan I made use of to handle the meter. USB was still taboo back then and was just mainly used for storage devices. 1N4001 is a good multi purpose diode. You might want to check that out. |
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codingplanet
Mad Scientist
United Kingdom
195 Posts |
Posted - Jun 15 2011 : 11:02:43 AM
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Johnny, my USB ports were damaged to some extent. While a USB stick works, my contraption still works if plugged into a different set of ports.
I put a cap across the 12v rail (100uF, I will use larger value when I find one). And as you predicted, the spikes are greatly reduced. I expect they will be gone if I use the suggested 470uF.
Here is the result of the 12v rail added to the voltage on the other side of the fan: http://i547.photobucket.com/albums/hh471/UnknownReactionz/100_1457.jpg
2v/div, 50uS timebase. |
Edited by - codingplanet on Jun 15 2011 11:03:09 AM |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Jun 15 2011 : 11:48:51 AM
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quote:
Originally posted by codingplanet
Johnny, my USB ports were damaged to some extent. While a USB stick works, my contraption still works if plugged into a different set of ports.
I put a cap across the 12v rail (100uF, I will use larger value when I find one). And as you predicted, the spikes are greatly reduced. I expect they will be gone if I use the suggested 470uF.
Here is the result of the 12v rail added to the voltage on the other side of the fan: http://i547.photobucket.com/albums/hh471/UnknownReactionz/100_1457.jpg
2v/div, 50uS timebase.
I hate hearing about computers being damaged - it breaks my heart.  Hehe.
Good to see you reduced your spikes. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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codingplanet
Mad Scientist
United Kingdom
195 Posts |
Posted - Jun 15 2011 : 11:56:16 AM
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| Don't worry, I have fixed it now :D Device manager was reporting an issue with the hub. After disabling and re-enabling it, there are no issues and the front USB ports work again :D |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Jun 15 2011 : 12:08:30 PM
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quote:
Originally posted by paulh
I think this can be really useful as you can see the temperature and voltage on the fly. I have tried a similar project before where in there is an extra bread pan I made use of to handle the meter. USB was still taboo back then and was just mainly used for storage devices. 1N4001 is a good multi purpose diode. You might want to check that out.
The 1N4001 is a good general purpose diode. However in the case of snubbing the inductive kick-back (flyback) of an energised coil of wire (a fan in this case), the need for a more specialised type of diode is required. The 1N4001 is not suitable because the need for a very quick transition from being reversed biased (most of the time) to becoming forward biased is required. Obviously the diode is only forward biased when it is snubbing the flyback. If you are so inclined and if you are fairly good at calculus, you can estimate the energy that will be wasted as heat through the snubber diode and maybe even guess at how hot it will get. I would do this kind of calculation because I am a N.E.R.D. (Not Even Remotely Dumb).
About Flyback Diodes:
http://en.wikipedia.org/wiki/Flyback_diode |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Jun 15 2011 : 12:10:57 PM
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quote:
Originally posted by codingplanet
Don't worry, I have fixed it now :D Device manager was reporting an issue with the hub. After disabling and re-enabling it, there are no issues and the front USB ports work again :D
That's great news Adrian. Hard to imagine damage can be caused merely by shorting out the 5V on a USB port. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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codingplanet
Mad Scientist
United Kingdom
195 Posts |
Posted - Aug 07 2011 : 10:38:54 AM
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Hi Johnny :D I've done a bit since we last spoke.
I bagged a few diodes from where I'm working. They are SBRs "super barrier rectifiers". SBR2A40 to be exact. They are rated for 2A continuous and are fast switching like schottkys.
I have found that for reading voltages on my PIC's 12bit ADC, a 10uF cap makes a good filter across the input. The wire that I am using between my voltage source and the PIC is about 0.5m long and seemed to be picking up a small amount of noise. The cap fixed this while making a negligible effect on the voltage reading response time.
I have also decided that I will use an instrumentation amplifier, probably an AD8553 to amplify my thermocouple's voltage. And I will use a linear digital temperature sensing IC to provide cold-point compensation within the PIC software. However, as I wish to measure temperatures down to -200C using a single 5V supply, I need to offset the input by 6mV. Looking at the AD8553 datasheet (http://www.analog.com/static/imported-files/data_sheets/AD8553.pdf) can I use the Vref input for this purpose? The problem I see is that the differential input voltage is spec'd between 0-3.3V and the Vref correction would happen after the input stage. If I can't use the Vref pin I guess I will have to provide the offset on the inverting input.
Oh, and I started using Eagle for my Schematics and PCBs as DesignSpark was starting to piss me off (libraries aren't logical and the program wouldn't start on one of my machines). |
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jnewman
Apprentice
United Kingdom
126 Posts |
Posted - Aug 09 2011 : 7:34:25 PM
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You using something like PL2303 USB to TTL serial to bridge the PC to the pic or implementing a USB stack in software (if I remember the PIC from my PICAXE days you are using is really just a PIC, no hardware USB?).
I am, or have now finished a similar project, using an AVR ATMega8 with a PL2303 USB/Serial and a DS1307 RTC over I2C. A computerised irrigation system where you can program all your timings along with the current time using a VB.NET frontend, hit save, it sends it over serial, the AVR saves it to it's EEPROM and sets the clock on the DS1307. The AVR then polls the time on the RTC every couple of seconds or so and compares it with the timings in the EEPROM in simple terms. The valve is simply connected to a MOSFET, along with a protection diode, then into the AVR with a pullup resistor.
on the dev board, the valve there not connected though. The AVR is on the STK500 dev board wired to the RTC which is on the breadboard.
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>>> http://www.josephn.net <<<
>>> http://forum.josephn.net <<< |
Edited by - jnewman on Aug 09 2011 7:36:18 PM |
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wasssup1990
Nobel Prize Winner
A Land Down Under
2261 Posts |
Posted - Aug 13 2011 : 07:16:16 AM
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quote:
Originally posted by codingplanet
Hi Johnny :D I've done a bit since we last spoke.
I bagged a few diodes from where I'm working. They are SBRs "super barrier rectifiers". SBR2A40 to be exact. They are rated for 2A continuous and are fast switching like schottkys.
I have found that for reading voltages on my PIC's 12bit ADC, a 10uF cap makes a good filter across the input. The wire that I am using between my voltage source and the PIC is about 0.5m long and seemed to be picking up a small amount of noise. The cap fixed this while making a negligible effect on the voltage reading response time.
I have also decided that I will use an instrumentation amplifier, probably an AD8553 to amplify my thermocouple's voltage. And I will use a linear digital temperature sensing IC to provide cold-point compensation within the PIC software. However, as I wish to measure temperatures down to -200C using a single 5V supply, I need to offset the input by 6mV. Looking at the AD8553 datasheet (http://www.analog.com/static/imported-files/data_sheets/AD8553.pdf) can I use the Vref input for this purpose? The problem I see is that the differential input voltage is spec'd between 0-3.3V and the Vref correction would happen after the input stage. If I can't use the Vref pin I guess I will have to provide the offset on the inverting input.
Oh, and I started using Eagle for my Schematics and PCBs as DesignSpark was starting to piss me off (libraries aren't logical and the program wouldn't start on one of my machines).
Hi Adrian, buddy.
I've been pretty busy lately so please forgive me if I miss anything.
VREF, according to the equation given on page 13 of your datasheet will offset the voltage of the output. If I understand you and the datasheet correctly, you will need to positively offset the VIN- by your predetermined voltage of 6mV.
So,
quote:
Originally posted by codingplanet
"the Vref correction would happen after the input stage"
Is correct.
quote:
Oh, and I started using Eagle for my Schematics and PCBs as DesignSpark was starting to piss me off (libraries aren't logical and the program wouldn't start on one of my machines).
I have given Eagle a try on several occasions. It's good but I am not paying for it, so I am left with a cut-down, free licence which sucks. It wont let me use multiple sheets. I tried to crack it with initial success but then I gave up. I have used Altium; it is very good but it is a huge program and I wanted something a little more simple to use that isn't as resource hungry. Now I am using Kicad; it ticks all the boxes for me so far. I always use a pen an paper or a Tablet computer to get ideas out of my head quickly though. Then I use a "schematic capture" program and expand upon my design. I used MS Paint once... yeah, I don't need to say any more. 
See ya. |
When one person suffers from a delusion it is called insanity.
When many people suffer from a delusion it is called religion. |
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USB contraption
