"Decoupling" two grounds - Page 1
Forum section: electronics / projects

author: raff5184
author_rank: Regular Contributor
timestamp: November 18, 2020, 03:44:46 pm
content: Hi,as in the attached simplified circuit I have a piezo transducer connected to a rectifier to recharge a capacitor. The capacitor powers a data transmitter (TX) that uses the same piezo to send data. Signals and waves are at 1MHz. The components work fine separately.My problem is obviously with the grounds. The Transmitter has only one ground (GND_t) that I connect to the capacitor pin C1-2, but I also need to connect it to the GND of the piezo. But the problem is that, in this way, the "-" of the rectifier output (i.e. C1-2) gets connected to GND (they should stay independent instead) and now it only rectifies half of the signal.Is there a way to "decouple" the grounds? I mean a way to connect the transmitter GND_t to C1-2 for power, and also have an "independent" line to GND, so that the data signals are referred to the piezo GND?

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: November 18, 2020, 04:01:32 pm
content: Use a DPDT switch, or a transformer to convert the single-ended TX output to balanced, so it no longer references GND.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 18, 2020, 04:11:58 pm
content: What is the transmitter? Does it not have a standard configuration for doing this?The usual solution would be an H-bridge driver, which either has the diodes internally (MOSFET body diodes) or activates the MOSFETs as needed to synchronously rectify incoming power. Which conversely can simply drive the piezo directly, for transmit. No diodes, no switches needed.Tim

author: raff5184
author_rank: Regular Contributor
timestamp: November 18, 2020, 06:12:47 pm
content: Quote from: T3sl4co1l on November 18, 2020, 04:11:58 pmIt's based on a microcontroller,https://www.nxp.com/docs/en/data-sheet/KL03P24M48SF0.pdfthat I don't think has this configuration.Quote from: radar_macgyver on November 18, 2020, 04:01:32 pmHow would the DPDT be connected? If I switch grounds I can either connect the TX to the capacitor or to the piezo, but not both at the same time

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: November 19, 2020, 05:39:54 am
content: This, or Tim's far more elegant method. What drives the need to have both the transmitter and the power supply connected at the same time?

author: raff5184
author_rank: Regular Contributor
timestamp: November 19, 2020, 02:42:20 pm
content: Quote from: radar_macgyver on November 19, 2020, 05:39:54 amah that's because the microcontroller (tx) does other functions, such as sensing, that can't be a interrupted.So if I understood correctly, also with the h-bridge I won't be able to have both at the same time?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 25, 2020, 09:27:23 pm
content: Why use a bridge rectum fryer in this circuit?Do you have some data about how much data the piezo thing generates?A charge pump with a voltage doubler may be a better choice, and this way you also have a common ground in the whole circuit.These days there are also specialized IC's for harvesting enery from low power devices

author: raff5184
author_rank: Regular Contributor
timestamp: November 25, 2020, 10:44:24 pm
content: Quote from: Doctorandus_P on November 25, 2020, 09:27:23 pmif the doubler works that'd be great because it'll solve my problem.But, isn't the charge pump an active component? I have no other energy sources on my system.What do you want to know about data specifically? Packet size, how often it sends data, bitrate?Yeah I tried some of those ICs but they don't work with piezo at 1Mhz and low power

author: raff5184
author_rank: Regular Contributor
timestamp: November 30, 2020, 04:05:26 am
content: Quote from: Doctorandus_P on November 25, 2020, 09:27:23 pmHi,I am trying to understand how this solution works. But I still don't know how it is supposed to be connected. Can you please provide a simple schematic? Did you mean I should use a single chip that integrates a charge pump with voltage doubler, or are they two separate circuits? Also isn't a charge pump a type of DC-DC converter? How does that work with a 1MHz periodic signal?thank you

author: KT88
author_rank: Frequent Contributor
timestamp: November 30, 2020, 12:47:05 pm
content: That was probably the idea...CheersAndreas