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Is it possible to run the Propeller Mini with 5v? — Parallax Forums

Is it possible to run the Propeller Mini with 5v?

JohnR2010JohnR2010 Posts: 431
edited 2014-09-16 23:06 in General Discussion
I have a project that requires more current than the 5v, 1a output of the propeller mini will source. I already have a 5v 3a source for my project and I would like to know if it is possible to not use the 6.5 to 12vDC Vin port of the propeller mini and just hook up my existing 5v to the 5 Vdc regulated output pin of the propeller mini? From looking at the schematics of the mini It looks like that will feed the internal 3.3 volt regulator and therefore power the propeller just fine.

I'm trying to eliminate the need for another 6.5v power source.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-09-15 13:43
    John,

    If you have a regulated 5V supply you should be able to connect that to the 5V pin on the Mini. I will double check that the regulator used can tolerate that.
  • David BetzDavid Betz Posts: 14,516
    edited 2014-09-15 13:47
    JohnR2010 wrote: »
    I have a project that requires more current than the 5v, 1a output of the propeller mini will source. I already have a 5v 3a source for my project and I would like to know if it is possible to not use the 6.5 to 12vDC Vin port of the propeller mini and just hook up my existing 5v to the 5 Vdc regulated output pin of the propeller mini? From looking at the schematics of the mini It looks like that will feed the internal 3.3 volt regulator and therefore power the propeller just fine.

    I'm trying to eliminate the need for another 6.5v power source.
    I've done this before and it worked but I'm not sure how safe it is. In particular, I'm not sure if there is any danger of frying the 5v regulator.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-09-15 14:00
    Most regulators have an open-collector/open-drain output are are safe to do this as long as you're not also powering them from the input. I thought I had a Mini here (home office) but I was mistaken. I will have to double check tomorrow when I am in the Rocklin office.

    By the way, this is how the BASIC Stamp Modules work. You can power them from VIN or VDD.
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-15 14:49
    Chris Savage wrote: »
    John,

    If you have a regulated 5V supply you should be able to connect that to the 5V pin on the Mini. I will double check that the regulator used can tolerate that.

    Thanks Chris let me know if your find-out otherwise. I just placed an order for a couple of units and I was going to try it but I thought I would ask and see if there were any concerns.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-09-15 14:54
    Okay John, I can get access to one tomorrow. I wanted to double check the regulator and verify it as the posted schematic seems to have an error in it and I am not sure which regulator is on that module.
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-15 15:30
    Chris Savage wrote: »
    Okay John, I can get access to one tomorrow. I wanted to double check the regulator and verify it as the posted schematic seems to have an error in it and I am not sure which regulator is on that module.

    Yep saw the same thing in the schematic. The drawing didn't match the parts list. I was thinking the parts list on the second page was correct but not sure. Thanks for looking into it!!
  • RDL2004RDL2004 Posts: 2,554
    edited 2014-09-16 01:42
    The issue of errors in the Propeller Mini's schematic has come up before. Apparently the schematic was changed, but even more errors were added. Please read this entire thread (started by David Betz which is also about running the Mini from 5 volts directly) for more details.

    http://forums.parallax.com/showthread.php/152334-Prop-Mini-power-supply

    The current schematic (Rev A version 1.2 1/28/2014) lists VR1 as an LM2940 in the BoM, but on the diagram it's shown as M24512. According to the BoM, VR2 is supposed to be a 3.3 volt LM2940, but it's shown as the 5 volt version on the diagram.

    As listed in the BoM, an M24512 is the eeprom. However, the schematic diagram shows a 24LC256 eeprom. I thought the Propeller Mini was supposed to have a 64KB eeprom, what is actually used?

    Basically the latest published schematic shows 2 (two) different eeprom chips but only 1 (one) regulator in the diagram, whereas the BoM lists one eeprom and two regulators. It seems the revised version 1.2 of the schematic added more errors than it fixed.
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-16 05:03
    RDL2004 wrote: »
    The issue of errors in the Propeller Mini's schematic has come up before. Apparently the schematic was changed, but even more errors were added. Please read this entire thread (started by David Betz which is also about running the Mini from 5 volts directly) for more details.

    http://forums.parallax.com/showthread.php/152334-Prop-Mini-power-supply

    The current schematic (Rev A version 1.2 1/28/2014) lists VR1 as an LM2940 in the BoM, but on the diagram it's shown as M24512. According to the BoM, VR2 is supposed to be a 3.3 volt LM2940, but it's shown as the 5 volt version on the diagram.

    As listed in the BoM, an M24512 is the eeprom. However, the schematic diagram shows a 24LC256 eeprom. I thought the Propeller Mini was supposed to have a 64KB eeprom, what is actually used?

    Basically the latest published schematic shows 2 (two) different eeprom chips but only 1 (one) regulator in the diagram, whereas the BoM lists one eeprom and two regulators. It seems the revised version 1.2 of the schematic added more errors than it fixed.

    Thanks Rick for pointing me to the previous post on this. I read through all three pages and saw suggestions from driving the Vin pin with 5v (far bellow the recommend voltage) to doing what I want to do by connecting 5v to the v-out pin. I would still very much like Chris to make a recommendation as I didn't see a definite answer. David Betz said he did this and it worked fine. David also asked if this could be done with the 3.3v v-out pin I have that same question.
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-16 05:09
    Chris Savage wrote: »
    Okay John, I can get access to one tomorrow. I wanted to double check the regulator and verify it as the posted schematic seems to have an error in it and I am not sure which regulator is on that module.

    Chris I have two questions now:
    1) If I want to drive my prop mini with an external regulated 5v power supply is it okay to connect it to the 5v v-out pin of the prop mini (no connection on Vin pin)?
    2) If I want to drive my prop mini with an external regulated 3.3v power supply is it okay to connect it to the 3.3 v-out pin (no connection on 5v v-out or Vin pins)?


    If your interested I'm going to use the Prop Min to drive Digi's xBee ZB SMT chip with a ZigBee Home Automation library I have written in SPIN.

    Here is a screen shot of the PCB I'm working on:
    PropMiniLayout.JPG


    Link to my ZigBee Home Automation post on your forum: http://forums.parallax.com/showthread.php/157233-Propeller-to-SmartThings-%28communicating-with-the-ZigBee-HA-public-profile%29

    Thanks!
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  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-16 05:11
    Loopy Byteloose wrote: »
    Hi John,
    I realize that the voltage regulator is rated at 1 amp output, but it also has a thermal shutdown if it gets too loaded. And since, the board is so tiny, I don't think you are going to get anywhere near 1 amp output from it.

    You would have to have it optimally configured with a big heat sink to do so.
    Yes I understand and this is why I'm asking if I can power the min from an external regulated 5v power source. Thanks.
  • RDL2004RDL2004 Posts: 2,554
    edited 2014-09-16 05:35
    If the regulators used are actually the LM2940, then there will be no problems. The LM2940 is an "automotive grade" part and is guaranteed to withstand up to 60 volts in reverse. However, as I pointed out above, the current Propeller Mini schematic actually shows the 5 volt input regulator as an M24512 eeprom. So yeah, best wait for Chris to figure out what's actually used.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-09-16 09:26
    John,

    It turns out I am not in Rocklin today. I took a couple days off. However, I am not going to leave you hanging. David Carrier should be in the office today and can get access to the complete internal information on the Prop Mini from our network. He can post a definitive answer for you. I am going to link your last questions post to him right now and then will follow up in a bit to see if he has been able to answer it. If not I will drive down to Rocklin today and get the information myself. :thumb:
  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2014-09-16 10:44
    Check out post #10 on this thread as well. The part marking on the Propeller Mini that I had was different but I was able to determine which equivalent one it was.
  • JonnyMacJonnyMac Posts: 9,186
    edited 2014-09-16 12:15
    I needed to do the same thing a couple months ago and didn't have any problems. In my case I was connecting 4.5v from a battery pack to the 5v terminal (with nothing on Vin) to run the Propeller mini in a little board that controlled a WS2812 strip in a dress made for a fashion show at Comic-Con 2014.
    prop-mini_carrier.jpg
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  • David CarrierDavid Carrier Posts: 294
    edited 2014-09-16 12:20
    I just checked the bill of materials in our inventory control system, and VR1 is an LM2940IMP-5.0/NOPB and VR2 is an LM2937IMP-3.3/NOPB. The current schematic shows VR1 as being from the wrong series, LM2937 instead of LM2940, but it is otherwise correct, including the voltage. I've updated the schematic and sent it off to our web department, so it should show up soon.

    Regard the original question of whether you can power the Propeller Mini's Vin pin with 5 VDC, it should work, but it will leave the 5-volt regulator in full dropout, so the power consumption will be a littler higher than normal. You can also connect the 5-volt supply to the 5V pin to power the Propeller Mini. It may leak some power into the Vin pin, so I recommend leaving the Vin pin unconnected.

    — David Carrier
    Parallax Inc.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2014-09-16 12:25
    Thanks David! I wanted to make sure John got his answer in a timely manner since I couldn't get the information today as planned.
  • RDL2004RDL2004 Posts: 2,554
    edited 2014-09-16 12:37
    The current schematic shows VR1 as being from the wrong series, LM2937 instead of LM2940, but it is otherwise correct, including the voltage.

    Sorry, that is not totally correct. Please read my post #9. The current schematic diagram shows VR1 as an M24512 and VR2 as a 5 volt LM2940.

    However, the BoM is correct according to your post, listing the part numbers for VR1 as an LM2940-5.0 and VR2 as an LM2937-3.3

    You should probably double check that the diagram and BoM in the new schematic agree.
  • David CarrierDavid Carrier Posts: 294
    edited 2014-09-16 13:21
    RDL2004,
    I meant to say and link to the original schematic, which wasn't too far off. I don't know what the v1.2 schematic was going for with the M24512 part number on VR1, since it is an EEPROM.

    Speaking of the EEPROM, I just notice that the schematic says that it is a 24LC256, but there is a good chance that it is an M24512. I'll check on that and update it if necessary.

    — David Carrier
    Parallax Inc.

    Edit: It is an M24512. That will be corrected on the updated schematic, too.
    Edit: The schematic is now up: http://www.parallax.com/sites/default/files/downloads/32150-Propeller-Mini-RevA-Schematic-v1.3.pdf
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-16 15:09
    Thanks David!!
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-16 15:11
    Thanks Chris for the follow-up!! Enjoy your time off!!
  • JohnR2010JohnR2010 Posts: 431
    edited 2014-09-16 15:20
    Thanks Jonny!! One of my first project is to use your jm_ws2812_demo.spin just wanted to say thanks for posting it!!
  • RDL2004RDL2004 Posts: 2,554
    edited 2014-09-16 23:06
    Looks good David. Thanks to you and Chris for seeing that these corrections were made.

    Unlike what Loupey seems to think, many of us still like to know what we are getting when we spend our hard earned money.
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