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camp david
Joined: 27 Jan 2015
Posts: 25
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 Posted: Thu Feb 19, 2015 8:16 am |
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A good explanation, the supply will be 3.3 for all devices.
I made my hardware already, I agree with you no simulator gives 100% result of the real circuit, but Proteus consider a nice pre-test.
temtronic POOF |
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kWoody_uk
Joined: 29 Jan 2015
Posts: 47
Location: United Kingdom
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| Posted: Thu Feb 19, 2015 8:32 am |
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I don't need an invitation as this is an open forum where any member can politely ask for help.
Thanks for inferring I'm young though; at 37 that's a compliment :-)
Keith |
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temtronic
Joined: 01 Jul 2010
Posts: 9243
Location: Greensville,Ontario
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| Posted: Thu Feb 19, 2015 8:43 am |
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If you post your Proteus schematic, I'll happily list you the errors that it makes compared to the real world. Some are basic based on 'assumptions' that the tech knows the devices they're using,others are PIC related.
I use this forum and 'play with PICs' to keep the old grey cells active. It's either here or shovel snow at 0*F!
Jay |
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camp david
Joined: 27 Jan 2015
Posts: 25
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| Posted: Thu Feb 19, 2015 8:49 am |
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| kWoody_uk wrote: | I don't need an invitation as this is an open forum where any member can politely ask for help.
Thanks for inferring I'm young though; at 37 that's a compliment :-)
Keith |
no need for thanx, everybody harvest what he planting
"any member can politely" treated when he does |
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camp david
Joined: 27 Jan 2015
Posts: 25
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| Posted: Thu Feb 19, 2015 9:05 am |
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temtronic, it's a simple 16f677 based circuit
from RB4 to RB7 connected to LCD #sck to #sres
4 wires out from pic to LCD, mclr of pic connected to vdd through 10k resistor no more.
Let me just make the changes suggested and see what would happen. |
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ELCouz
Joined: 18 Jul 2007
Posts: 427
Location: Montreal,Quebec
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| Posted: Sun Feb 22, 2015 8:12 am |
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| temtronic wrote: | All it takes is 15 minutes of reading the datasheets of the devices and seeing that a logic '1' from a 3 volt device will NEVER be a logic '1' into a 5 volt device
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Not true Jay,
| Code: | TTL threshold voltage is defined (per specs)
LOW --> 0 V to 0.8 V
HIGH --> 2 V to VCC |
Even if the 5v device receive a 3.3v HIGH signal, it will still be able to register it has 1...
The other way, you need to be double sure that the 3.3v device is 5V tolerant!! Otherwise, the 3.3v device will do some magic blue smoke!
Just wanted to clarify, nothing personal Jay! 
Keep up the good work & have a nice day!
_________________
Regards,
Laurent
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Here's my first visual theme for the CCS C Compiler. Enjoy! |
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temtronic
Joined: 01 Jul 2010
Posts: 9243
Location: Greensville,Ontario
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| Posted: Sun Feb 22, 2015 9:47 am |
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Yeah PICs are pretty good BUT it's the garbage can that can get FULL real quick when you apply 5 volts to 3 v 'devices'.
For some reason they heat up fast and let out the 'magic smoke'.
The simplest, easiest way to be sure PIC and peripheral 'like each other' is to run from the same supply.
If you get 'lucky' and it may work this time BUT next time, the expensive 3V peripheral WILL blow up..Murphy says so ! I'm just saying that if you get into the habit of 3v for everything, life is simpler.
The other issue is timing.... that PIC will not run at 16MHz at 3 volts.
Jay |
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dyeatman
Joined: 06 Sep 2003
Posts: 1934
Location: Norman, OK
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| Posted: Sun Feb 22, 2015 1:51 pm |
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Of course there is the 'other" option to frying the display which is to use level translators.
Then he can run the PIC at 5V (and max speed) and the display at 3V.
I have done this on numerous occasions.
_________________
Google and Forum Search are some of your best tools!!!! |
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ELCouz
Joined: 18 Jul 2007
Posts: 427
Location: Montreal,Quebec
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| Posted: Sun Feb 22, 2015 2:10 pm |
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| dyeatman wrote: | Of course there is the 'other" option to frying the display which is to use level translators.
Then he can run the PIC at 5V (and max speed) and the display at 3V.
I have done this on numerous occasions. |
Depending on the complexity of the thing (how many bus lines),
you can do it with simple transistors otherwise it is better to use some level shifting IC!
The Texas Instrument 74LVC245 is an example...
Or also voltage dividers is doable...
_________________
Regards,
Laurent
-----------
Here's my first visual theme for the CCS C Compiler. Enjoy! |
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dyeatman
Joined: 06 Sep 2003
Posts: 1934
Location: Norman, OK
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| Posted: Sun Feb 22, 2015 2:53 pm |
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| Quote: | The Texas Instrument 74LVC245 is an example...
Or also voltage dividers is doable... |
I fully agree on the 74LVC245, I have used it a couple of times but I prefer
the 2N7000 FET if real estate is not an issue.
Voltage dividers for outputs are OK but inputs are another story.
_________________
Google and Forum Search are some of your best tools!!!! |
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temtronic
Joined: 01 Jul 2010
Posts: 9243
Location: Greensville,Ontario
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| Posted: Sun Feb 22, 2015 3:18 pm |
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I still like the KISS method( Keep It Simple, Silly) of 3V PIC and 3 V peripherals. Eliminates all the interface issues(part selection,inventory,PCB layout, revisions,overall cost,etc.)
Too bad no one sell cheap9$5 for 4x40) 3v driven LCD modules.
Jay |
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ELCouz
Joined: 18 Jul 2007
Posts: 427
Location: Montreal,Quebec
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| Posted: Sun Feb 22, 2015 3:27 pm |
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| temtronic wrote: | I still like the KISS method( Keep It Simple, Silly) of 3V PIC and 3 V peripherals. Eliminates all the interface issues(part selection,inventory,PCB layout, revisions,overall cost,etc.)
Too bad no one sell cheap9$5 for 4x40) 3v driven LCD modules.
Jay |
Yeah but sometimes it's not possible...
Like when you need more firepower (ex: dsPIC33/PIC24 series [3.3V]) and you have some old tech sensors to read (5V)... running at the same voltage in this case is impossible and you would need level shifting...
Luckily some dsPIC33/PIC24 are 5V tolerant on digital inputs but that's about it!
KISS is great when you can do it! 
_________________
Regards,
Laurent
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Here's my first visual theme for the CCS C Compiler. Enjoy! |
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