New Hardware Designs

I just finished the porting work of my Compact Lora Messenger (loramessenger:project [Unit Engineering Wiki]) to meshtastic, I added GPS support to this pocket size design.

I can’t produce this design due to Chinese New Year, thus I am working on the “Station” edition which has 1 stage PA for at least 33dBm to 36dBm TX power. This edition has SMA connector for supporting external antenna so that it named “station”. I am considering to design the new device without GPS support. I wonder is the GPS function necessary for the meshtastic devices, if almost all phone has GPS?

By the way, just as brainstorm, past 10 years I designed a lot of IOT devices for smart home applications, those devices based on Zigbee mesh. I thought meshtastic may have its advantages for smart city or smart farm applications.



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Plans 868 for Europe?
external antenna connector or PCB trace to solder on?
Large display?

Hi,
For current nano edition, it could be tuned to EU 868 MHz band by adding several 0402 components for the antenna matching.

External antenna could also by supported, however I haven’t found a clear advantage of external antennas for low power handheld devices. :sweat_smile:

For the OLED, I think there is also no clear difference between 0.96 inch and 1.3 inch. I just used to use 1.3inch oled :grin:

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When have old eyes above age 50+ you will understand the larger display 100% sure of that :slight_smile: :slight_smile:
Antenna matching a particular freq, have better resonance and range as wire or pcb antenna. Very simple example, 915 MHz when pump 100 watts in 5 cm wire, nobody hear me. Pump 100 Watts in simple dipole antenna, range be up 30++ km. My personal experience a PCB antenna combination with 2 or 4 C’s are a impedance matching network to match 50 Ohm or other impedance value and to preventing RF stage above 20 dBm not overheating or blown out (SWR matching bridge).

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You are correct about the antenna matching, as the result the 915Mhz antenna could be matched to EU868Mhz band for acceptable radiation efficiency. It will be not able to match to 433Mhz.

During the design process, I measured and modeled all RF switch, LNA, caps and inductors (e.g. rfmeasurement:testing_fixture_6_lead_qfn_spdt_rf_switch [Unit Engineering Wiki]). According to the models, the RF front end could support EU band with slight performance downgrade, but the current version PCB antenna could not work under EU band without matching (The antenna’s S11 measurement and Radiation Pattern loramessenger:project [Unit Engineering Wiki]). According to the antenna’s S11, the impedance bandwidth is unable to cover the EU band without matching, even the RF front end already support EU band :joy:

I plan to design a PCB antenna which could support 433, 868 and 915 Mhz in the same time by using helix‐loaded whip technology, this antenna could provide wider impedance bandwidth in EU and US bands. However the footprint will be larger than current design, it will be used in high power version for better performance when near human body or metals.

For the screen, I never used 0.96inch OLED… it seems it is just slightly smaller than 1.3inch :sweat_smile: I do tried to find the bigger SH1106 oled screen, it seem 1.3inch was only one I could find. :smile:

Thank you, All those measurement are done in ideal lab conditions (RF rooms). PCB antennas, when point your finger to it, lay down on a surface, or wave with your hand nearby, or build in a box, the VSWR and pattern changes instantly. Simple test anyone can do, put on the roof of your car, drive around you see fluctuations VSWR causing from surrounding objects. I not like to be “know all” but after 48 years repair and build many type antennas from 1 MHz to 24 GHz, i have seen the antenna is the end key to get more range. Most topic in this forum, that power give range, while the antenna is the end factor doing the actual radiation. Radiation pattern 868 to 915 MHz base antenna

Lets move on and not repeating myself, when this PCB be evaluated?

Totally agree, antenna is key for coverage. For the antenna near human , this currently is a hot research area especially for wearable device. Wider impedance bandwidth only could reduce this problem, it cannot be completely solved. For the low TX power device, wider impedance bandwidth could be a suitable solution. However, for the High Power Handheld Device, I have to implement directional coupler for VSWR measurement in the realtime, the VSWR will be used to control the reconfigurable antenna/tuner for the best radiation efficiency possible. I have to do this for RF mosfet protection, because I don’t want to use RF circulator.

Following content is what I reply to a forum member, from my viewpoint, the antenna problem could finally be solved until Pro edition come out, I hope I could reach that point ASAP :rofl::

I plan to design 3 series of device, I mainly focus on RF optimization.

Nano(First device is waiting for production):
pocket size, PCB antenna, with LNA, GPS.

Station (4W version is under designing stage):
2W to 50W PA+LNA, SMA connector, with/without GPS (No final decision yet)

Pro (Planning):
pocket size( maybe a little bit larger), enhanced impedance bandwidth PCB antenna (could work better when near human body or metals, Reconfigurable antenna/tuner technology may also used in this design), with 2W to 5W PA+LNA, GPS.

This design will be evaluated after Chinese New Year, it is waiting for sample production now.

For the compact design, I could not use smart antenna technology due to footprint. I have to measure the Er of PCB and case materials (multi method used, here is one of them: rfmeasurement:ringresonatormethod [Unit Engineering Wiki]). I accurately model the entire design, including the antenna. The antenna has better performance once no metal near it. According to my previous test, the well designed simple antenna could reach at lest 1.5km coverage in the urban area((TX:14dBm, Freq:915Mhz, Spreading Factor:12)). I simply put the device in my pants pocket. Not bad for a low power pocket size device, I think. :joy:

For rising the power, according to the RF link budget, rising the power do could improve the coverage, using high gain antenna also works. However, how to design high gain antenna with acceptable footprint? This will be the final practical question. Directional antennas do not always fit the application scenario. Multiple antenna elements can flatten the radiation pattern, rising the gain in xy plane, however more elements also means larger footprint especially for low frequency band such as sub 1G.

If we already has the well designed rf front end and antenna, rising the TX power and reducing the RX noise figure are the almost only two factors we could improve. :joy:

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If you search for OLED I2C 2.42 , you will find bigger displays that are 2.42 inch.
They are readable for everyone without a magnifier :grinning:

I have already tried and it will work with meshtastic on T-beam boards, have not tried other boards.

This display usually has 7 connector pads and it can be switched between I2C and SPI mode.
Also two connector-pins have to be grounded and the reset needs a capacitor.

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“magnifier” :slight_smile: This oldy is interested for that 2.42, how, where

I bought mine at aliexpress

for instance this seller: TZT 2.4" 2.42 inch 128x64 OLED LCD Display Module SSD1309 12864 7 Pin SPI/IIC I2C Serial Interface for Arduino UNO R3 C51|LCD Modules| - AliExpress

“Er of PCB and case materials” there are solutions in the high power and High GHz range using PCB made of glas/ceramic component, very thin and fragile but often used (i forgot the name - old men moment). Understand your part about human body i not very familiar with that because i learned in the past, to keep away from near field high power devices close to human body and special attention to the “men hood” of us and the eyes :slight_smile: :slight_smile: I just look to the “normal” base / mobile station antenna situation. I fallow your product with great interest.

Great tip my friend, thank you because cant read those tiny txt. Is this work on the Tbeam tityGo boards? Standard 4 connection pin like the oled or use the GPIO?

“how to design high gain antenna with acceptable footprint”
Using PCB or ceramic 4, 8, 16 patch antennas and coupler using 50 Ohm line transformer on PCB. Put 4 of those PCB in square and you have a high gain nearly circular antenna. Its how those Cellular work. I use several of these on 900, 1500, 2400, 5800 MHz
Cut corner LHCP, RHCP and Vertical

Or use the same design as PCB Collinear vertical

I see there are different versions for sale a.t.m. v3.1 and see also v4.2. I bought mine a few years ago and I don’t know the version of my board. It looks different now.

Standard they are delivered in SPI mode and for I2C mode you have to replace a few resistors, some may be zero ohm. It is printed on the component side but documentation is (as often) not very good.

I’m doing this from memory so may be inaccurate, DC and CS needs to be grounded and RES is reset needs a cap of 1uF. SDA and SCLK are the I2C connectione SDA and SCL.
If I’m at home again next week I can look that up.

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@Neil

I like the design you made, very good thought out. Specially the splitting in TX and RX with the LNA giving 5dB noise improvement looks promising.

Making Meshtastic work on this board must be achievable, the only fix needed seems the antenna_switch signal on GPIO33. I think some extra lines of code are needed for this.

edit.
I read in your first post that you already did all the work for making this work with Meshtastic.
Amazing work you did.

Patch antenna array, usually has to be directional. It is very promising for mmwave radar, 5G but all of them have higher carrier frequency than sub 1g.

I described the design method of 24Ghz patch antenna with parallel feeding for radar application here:
https://uniteng.com/index.php/2020/08/13/introduction-to-patch-antenna-array-with-a-parallel-feeding-network/

Following two photos are what I designed for 24GHz radars.


Parallel feeding network

Serial Feeding network with side lobe control.

The footprint are all 5cm * 5cm.

Here is the calculator for the single patch:
https://www.pasternack.com/t-calculator-microstrip-ant.aspx

Imagine the footprint for a sub 1G 4 patches antenna array based on PCB, the footprint may larger then a 15inch laptop.Still too big for handheld devices. There are some application scenarios for base stations.

Ceramic could not solve all problems.

  1. for the small volume of production, TLCC antenna may reach >1000 bucks/pc due to the relative large footprint for sub1g application
  2. HTCC could not be used to implemented multi layer design, relative narrow bandwidth.could be improved by using slot feeding but that technology requiring multi layer structure.
  3. The small patch antenna usually have terrible TX efficiency, think about GPS antenna, about 1.5GHz, why no one use them to implement long range duplex communication.

For sub 1G application, patch antenna array is not small enough for handheld devices,

However, due to human curiosity, we will continue to look for feasible solutions. If found, we should be remembered by history due to promoting the popularity of wearable device. :joy:

In my spare time I’m digging in metamaterial antennas about reducing antenna size. No clue yet :sweat_smile:

Thanks costo,
I reconfigured the PINs by referencing TTGO T3_V1.6 except for the user botton. I don’t want to fragment the firmware version. :joy:

I skimmed what you guys have been taking about and find this very exciting.

I was wondering if you have seen these: Dipole Antenna 868-915mhz

Would it be possible to make a pcb antenna where we could cut the trace to tune the frequency?

Great to see lowpowerlab.com founded by ASU alumni.
Yes, it is possible to increase the resonant frequency by cutting the length of the antenna element. In other words, it is only possible to adjust the resonant freq toward higher frequency. However, the adjustment is usually within a very small range. Adjusting over a wide range usually results in a reduction in radiation efficiency.