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Help Please - Trouble with Bluetooth

I just received and assembled one of the new kits for glass scales.  The assembly went fine and after I powered it up I cannot not see the HC-05 listed in the Bluetooth setup from any device.  This is what is see:
  • The green Power LED is on solid
  • The green HB LED is flashing at once per second
  • The red bluetooth LED is flashing at 5 times per second
  • I have checked all solder joints with a jewelers loop and see no bridges or gaps.
  • I measure with voltmeter the following:
           7.21 volts at the power jack
           5.12 volts across the Bluetooth module VCC and GND
           3.34 volts across the two connections on the edge of the board labeled +3.3v and GND

Other noteworthy items...
  •      I did not solder the bluetooth module to the board, I used the 4-pin header and plugged the board using the ribbon cable. 
  •      I have not attempted to connect any scales yet.
  •      I have several wall warts laying around the are labeled 9 volts from 300mA to 1000mA.  Prior to energizing the board, I measured the voltage of the wall warts at around 13-14 volts.  Knowing the voltage needs to be between 7.5 and 9 volts, I was reluctant to use these wall worts.  I have another wall wart that is labeled 6.0 volts at 400mA that measures 8.4 volts with my meter.  I used this wall wart and once connected measures 7.21 volts under load.  I read that the LM1117 regulator is tolerant to 15 volts but did not want to exceed the 9 volts specified by Yuriy.  

Everything I see so far appears to be correct (connections, voltages, LEDs, etc) except that I cannot see the HC-05 show up on any device (Lenovo Android tablet, Iphone, Ipad, and Mac book).

Anyone seen this before??  thoughts??

Thank you,  Kenny Logsdon


Hello again,

I think I may have figured this out. I replaced the 6.0 volt wall wart with a 9 volt battery and now I see the HC-05 shows up on in the bluetooth settings. I am able now to pair with it and the TouchDRO app on the tablet is connected. This proves there is no hardware fault with the bluetooth module and that is good news. I think I have a low voltage issue. I have a wall wart rated at 9 volts & 600mA. The no-load voltage measures at 14.02 volts. I am wondering if this wall wart is within the acceptable voltage band but I am still reluctant to connect it up. The two other 9 volt wall warts I have all measure about the same with no load. Should I look for a 7.2 volt wall wart? I think once I connect three sets of glass scales I will see further voltage drop.

Thanks, Kenny Logsdon
In theory, the board should survive 15V (and probably more), since I pretty seriously de-rated the caps. That said, LM1117 are linear regulators, so they burn off the excess voltage as heat. Your delta-V will be 9V and 10.7V respectively, so you will be dissipating about 1W of heat per regulator. This is not fatal, but heat shortens the life of the components.
You'd be better off finding a regulated 7.2V power supply (they sell for a few dollars on eBay and Amazon).


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