STM32F103 BPSK

jean-paul Thu Aug 10, 2017 8:39 pm

Hello,

I’d like to do BPSK with a Blue Pill board for an ultrasound project.

I managed to generate a 40KHz PWM signal and I’d like to modulate the phase of each pulse (10-30 pulses max). Do you think it’s possible with a STM32F1? I saw this project https://github.com/ChrisMicro/BluePillSound/ where it’s generating several king of signal but it’s working at lower frequencies.

Thanks a lot,
Jean-Paul

Replies

jean-paul Sat Aug 12, 2017 7:10 pm

Oh ok I see.
This is what I got:
Sent pulse
Image
Sent and receiced at around 1.7m, with 20ms data.
Image

I think the US has problem doing 180° phase shift. I think it’s better to do frequency shift but these sensors are low bandwith.

Jean-Paul

ChrisMicro Sat Aug 12, 2017 9:51 pm

Nice pictures. My impression is that the transducers are neither suitable for phase coding nor for frequency coding. They have a too large self resonance.
If you goal is to realize indoor positioning the new way is using UWB time of flight measurement. There are now the first application boards also usable with Arduino:
https://www.decawave.com/products/overview

RogerClark Sat Aug 12, 2017 10:03 pm

Decawave looks interesting, but is quite expensive.

Another option is the laser based Time Of Flight devices from STM.
There is another thread about using these,
I have some of the long range version, but the range is limited to below 2m

jean-paul Sun Aug 13, 2017 11:31 am

Yes you are right, I tried to send another frequency and it resonantes at a different one with a lot of harmonics!

FFT of pulses at 41 KHz
Image

FFT of pulses at 44 KHz
Image

I need to find a better transducer…

ChrisMicro Mon Aug 14, 2017 2:55 pm

I’m just looking for the schematic of the HC-SR04.
Could this be the right one?
Image

jean-paul Wed Aug 16, 2017 6:35 am

Hello,

Yes I think it’s right. But on mine I don’t have the 2 transistors!

zmemw16 Wed Aug 16, 2017 3:31 pm

i’ve seen smd packages with complementary transistors in them.
srp

ChrisMicro Thu Aug 17, 2017 5:06 am

Yes I think it’s right. But on mine I don’t have the 2 transistors!
I think Q1 is only for threshold level adaption which is probably not really necessary and Q2 is for power saving which they removed to save costs.
The interesting point is the MAX232 RS232 driver which they misuse as sender driver.