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I'm trying to design a basic "very cheap" bluetooth solution, that can connect to my phone and turn on a light emitting diode via a signal.

The cheapest BLE IC I could find was this one on LCSC by Jieli Tech.

Part Name: JieLi Tech AC6329C4

Reference Design PDF

The documentation is bleak and incongruous. There is a github repo with a reference schematic from the manufacturer but never having worked with bluetooth or this chip before I can't tell what I need and what I don't.

My Schematic:

enter image description here

  1. I've tried to majorly use JLCPCB Basic Parts.
  2. The headers are for debugging incase of something going wrong.

Please let me know of any mistakes/ stupid connections candidly I appreciate the feedback and the help.

Edit following an answer: The battery was on backwards, that has been fixed. The connection to R16 has also been fixed and is now properly connected. The capacitor in series to the supply has also been fixed thanks to everyone's support.

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  • \$\begingroup\$ Since the circuit is not big, I think it will be better if you try it on a breadboard first. If it works properly, then you can make a PCB. \$\endgroup\$
    – liaifat85
    Commented Mar 21 at 15:32
  • \$\begingroup\$ @liaifat85 I would be very concerned about the effect a breadboard has on 2.4 GHz signals (i.e. the antenna) as well as the crystal signal. There's a good chance the capacitance and other parasitics will be far too great. \$\endgroup\$
    – nanofarad
    Commented Mar 21 at 15:41
  • \$\begingroup\$ The PCB frees my headache up quite a bit, and living in India, shipping the parts and getting the pcb will take the same amount of time. Plus this is a prototype to develop on the IC and play around with the sdk, therefore I'm just looking for feedback on the initial schematic. \$\endgroup\$
    – Mustansir Godhrawala
    Commented Mar 21 at 15:43
  • \$\begingroup\$ How did it go? Did you manage to get a working PCB? \$\endgroup\$
    – Jon Nordby
    Commented Jun 10 at 22:22

2 Answers 2

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I've added a couple of observations that look like faults to me: -

enter image description here

Should Vss to to GND/0 volts. I can't tell because of my next point.

You should choose parts that have pdf format data sheets and supplied by recognized dealers from a manufacturer who has a recognized quality policy.

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    \$\begingroup\$ Is the battery backwards too? (Not that it's powering anything for now.) \$\endgroup\$
    – Transistor
    Commented Mar 21 at 16:23
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    \$\begingroup\$ @Transistor it sure looks that way but, never mind cause the cap and diode will protect the circuit. \$\endgroup\$
    – Andy aka
    Commented Mar 21 at 16:24
  • \$\begingroup\$ Hey guys, yeah the battery was on backwards, fixed that after the post. I added the cap to do some "filtering" as was recommended. The red dot shows the connection to the led. The VDD should not be connected to ground? It was shown like that in the reference design, why is that? \$\endgroup\$
    – Mustansir Godhrawala
    Commented Mar 21 at 16:49
  • \$\begingroup\$ @MustansirGodhrawala I can't tell you why the reference design had this error other than to say it is a likely error. The red dot should not indicate that the LED is connected at that point else the 330 ohm resistor is shorted. The cap will prevent supply getting to the chip. I expect that any recommendation on this cap didn't mean for you to put it in series with the supply and, Vdd should be connected to the supply but, given that there is no data sheet link to the oscillator, I cannot be 100% sure. \$\endgroup\$
    – Andy aka
    Commented Mar 21 at 17:19
  • \$\begingroup\$ Thanks for your quick reply Andy, here's a link to the crystal's datasheet from LCSC lcsc.com/product-detail/… \$\endgroup\$
    – Mustansir Godhrawala
    Commented Mar 21 at 17:30
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  1. Add 2 loading capacitors to your crystal. Even if you don't use them, it is good to have empty pads, so you can adjust them. Their size should be 0603 or smaller.
  2. Add a pi impedance matching (two shunt and one in series) to the antenna net. Same as above, Either 0603 parts or 0402.
  3. Add a U.FL or an SMA connector for external antenna - This will allow you to connect a VNA to test your matching easily.
  4. Pay attention to your PCB stack-up and calculate the traces per your PCB manufacturer's recommendations.
  5. Optional: Consider using parts with proper datasheets from reputable manufacturers. These might cost you more per part, but save your time.
  6. Edit: The reference design uses a crystal with 12pF CL and 10ppm accuracy. you should use that instead of the oscillator. Your oscillator outputs square wave at CMOS levels, it will generate harmonics which will interfere with the IC. The design also has a PI network to match the RF output to a 50Ohm antenna. You must add that network, otherwise, you will not receive anything.
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  • \$\begingroup\$ What parts are you referring to? The ble modules is pretty much the cheapest I could find around for a reason, being a student I can spend the time on this, but not when producing 100-200 of these for the final project. Plus it's just a good challenge. \$\endgroup\$
    – Mustansir Godhrawala
    Commented Mar 21 at 16:51
  • \$\begingroup\$ An equivalent part from a tier 1 manufacturer (TI, ST, NXP and others) will cost you 2USD instead of 0.6USD. For 1000 units, that's 1400$ difference. Add a board respin, your time and frustration and decide if it is worth 1400$. \$\endgroup\$
    – Lior Bilia
    Commented Mar 21 at 19:34
  • \$\begingroup\$ $1400 is about around 1,16,000 INR, around 4 months of pay for an average engineer from where I come. Sure I can afford to spend that $1400 but the attitude might not be super sustainable for every decision I make. \$\endgroup\$
    – Mustansir Godhrawala
    Commented Mar 21 at 20:58

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