Working with the NRF8001 BLE Chip. First time using a balun, not working :( - Page 1
Forum section: electronics / rf-microwave

author: polishdude20
author_rank: Contributor
timestamp: October 12, 2020, 05:17:49 am
content: I've successfully been able to get the NRF8001 to work on a breakout board I made using their reference PCB design but I thought I'd use a balun for a new application to save on components. I just put together my new design and it communicates fine with my MCU and even confirms that advertising the connection has started but nothing shows up on my scanner on my phone. I'm not sure what is wrong with it and I have a suspicion that it's RF related. Can anyone give me some insight into what I could have done wrong?I've attached the schematic I made, PCB reference and real life photo of the circuit.The photo of the circuit is after I cut the antenna trace to see if that was the issue.I've seen on a few balun designs that you still need to match the antenna using a capacitor between the feedline and ground? Would not having this make it completely not work?EDIT: It turned out the 16Mhz crystal was the issue. It has a tolerance of +/- 0.08% which is way higher than the required 40ppm. I soldered on a better crystal with +/- 40ppm and it works great now!

author: daqq
author_rank: Super Contributor
timestamp: October 12, 2020, 06:44:35 am
content: What is the part number of the balun?

author: polishdude20
author_rank: Contributor
timestamp: October 12, 2020, 06:58:38 am
content: This is the balun:https://www.digikey.ca/en/products/detail/johanson-technology-inc/2450BM14A0002T/4770684?s=N4IgTCBcDaIOwEYwFoEFY4BZXIHIBEQBdAXyA

author: jan48
author_rank: Newbie
timestamp: October 12, 2020, 09:43:15 am
content: No DC is supplied to pin 20 (VDD_PA) of the IC. The balun chip is not a DC source!

author: mayor
author_rank: Regular Contributor
timestamp: October 12, 2020, 11:01:45 am
content: Hi, the output circuit looks good to me. I work (as a hobbyist, mind!) with Johanson baluns with TI CC13XX chips, and the output is very similar to that of the NRF chip you're using.Have you looked at the guidelines provided here?https://www.johansontechnology.com/downloads/app-notes/nRF8001-app-note.pdfThey recommend 2mm distance from NRF to balun, among other things. I don't think this would explain no communication at all, though.In my case, there was a small frequency offset due to capacitance loading of the HF crystal. In your case, there is no antenna matching circuit. In my experience, you will get very poor performance if you don't match the antenna (using a VNA, ideally). Do you have any means of doing conducted tests or access to a spectrum analyzer?

author: nali
author_rank: Frequent Contributor
timestamp: October 12, 2020, 12:07:56 pm
content: It's hard to tell from the photo, but the top RH lands (17&18) don't look properly soldered to me?

author: Heartbreaker
author_rank: Unknown
timestamp: October 12, 2020, 04:09:18 pm
content: Your 16MHz source looks like a cheramic resonator to me. The clock source must be 16MHz +/- 40ppm to make a reliable RF link. Normally you place a set of load capacitors across a crystal to tune the frequency to within 40ppm.

author: polishdude20
author_rank: Contributor
timestamp: October 12, 2020, 05:52:32 pm
content: Quote from: Heartbreaker on October 12, 2020, 04:09:18 pmYeah I got the same response from the Nordic Semiconductor forum. The crystal I use is this one:https://www.digikey.ca/en/products/detail/murata-electronics/CSTNE16M0V530000R0/8747756Looks like a stability of +-0.3% which for 16MHz is crazy high. I thought I'd use this one because it says it's got included capacitors so I thought I wouldn't have to add external onesThat's what I get for being greedy with space I suppose!