HC12 Range issues @ 115200 baud

Using Arduino Networking, Protocols, and Devices
1

Hi,
I'm using HC12 modules with stubby antennae for 433MHz to send serial data from a handheld Arduino controller to a number of receivers, and I need to get 50m in clear LOS with little or no data loss.
However, I'm experiencing major issues of losses outside of 25m which seems just plain wrong.

I've been reading up on antenna requirements and will probably construct a 1/2 wave dipole at the rx end(s) to help extend the range, but from all I've been reading about the modules I shouldn't be having such shortened range in the first place.

According to the data-sheets, specs and forum entries I'm seeing I should expect 100m easily.
Has anyone else had similar issues and managed to overcome them?

A little detail:
Tx:
Housing of the handheld control unit - plastic, compact.
Connected to HC12 Tx:
100uf capacitor.
Arduino; OLED screen, RFID module and 2S Lipo battery(~8v) in the same box.
Power for the HC12 is taken from the Arduino 5v supply point along with the OLED.
Stubby antenna mounted on outside of housing

Rx:
Housing - Plastic, roomy.
Connected to HC12 Rx:
Led matrix and associated driver module which requires 115200baud, not selectable unfortunately.
Arduino (incidental to main data-stream, only occasionally addressed) series connected to same data-stream from HC12 as the Matrix driver, 30cm lead.
12v Gel-Cell Battery, 5v 12A psu and piezo sounder
Stubby antenna mounted outside of box.

The antennae are in same polar plane.
The boxes, being plastic, do not provide a ground-plane. Is this part of my issues?

The data consists of simple serial text-based commands, sent with the objective of updating the LED matrix every second with a new number. I do no handshake, the HC12 modules in the Rx units are set to lowest gain so they have no impact on the other Rx units and they are expected to act as dumb serial pass-throughs. The Tx module is set to P8 which is the highest output power.
All works just fine within 25m, but begins to show package losses beyond, failing miserably by 30m.

I have experimented with different stubbies and, on a hunch, with wrapping the Tx HC12 in foil in case it was interference from the OLED or RFID modules - foil got me 2m more.

Settings:
C1
FU3
115200
P8(Tx) and P1(Rx)

Any help, or indication where I might find a solution, would be greatly appreciated.

2

The Hc12 can draw in excess of 100 ma when transmitting so needs its own power supply, and the stubby helical antennas have very poor range.
Use at least a 17 cm 1/4 wave antenna.

3

I have used these with good results for longer LOS 433 stuff.

goo.gl/cWUxBV

4

Dont waste your time with 'stubby' antennas.

Use antennas where the performance is at least predictable, 1/4 wave vertical with a ground plane or radials, or a dipole.

5

wzaggle:
I have used these with good results for longer LOS 433 stuff.

goo.gl/cWUxBV

For UHF yagis, I would highly recommned these;

http://www.arrowantennas.com/arrowii/440-7ii.html

I used one for some extreme long range LOS stuff.

6

mauried:
The Hc12 can draw in excess of 100 ma when transmitting so needs its own power supply, and the stubby helical antennas have very poor range.
Use at least a 17 cm 1/4 wave antenna.

You did see that I was applying this to a hand-held device? 17cm might just be a deal-breaker. In use these controllers could be worn around the neck on a lanyard, or on a belt. I will try it out though and see what difference it makes.

Of more interest to me would be any insights regarding ground planes, or the lack of them, on my plastic enclosures.

wzaggle:
I have used these with good results for longer LOS 433 stuff.

goo.gl/cWUxBV

You see my problem with these considering the above?
I didn't mention specifically but by its nature a hand held device would hardly lend itself to such an antenna array and still be considered useful.

These will be used in the field of sport as timer control modules, by the judges or coaches, and need to be user friendly.

srnet:
Dont waste your time with 'stubby' antennas.

Use antennas where the performance is at least predictable, 1/4 wave vertical with a ground plane or radials, or a dipole.

How is a ground plane designed with ref. to the aerial used?

7

OldManNoob:
How is a ground plane designed with ref. to the aerial used?

Plenty of information to be found on-line, look for stuff about ground planes and 1/4 wave radials.

As I suggested dump the stubby antennas and measure the performance of the HC12s with an antenna of know performance. Solve one problem at a time.

This sounds like a commercial product so do you have much experience in designing commercial products ?

Of particular concern is your suggested use of a 2S LiPo as the power source ...............

8

srnet:
Of particular concern is your suggested use of a 2S LiPo as the power source ...............

I'm using 2x 18650 cells - same as laptops use, with a power management routine to ensure the do not over-discharge.

Would that still cause concern?

9

OldManNoob:
I'm using 2x 18650 cells - same as laptops use, with a power management routine to ensure the do not over-discharge.

Would that still cause concern?

Depends.

What you need is some circuitry that cuts or switches off the connection to the battery.

The batteries might have an additional internal cut out, but its too low, 2.4V or so.

Far easier to use AAs as Alkaline or NiMh, do not underestimate the difficulty of using Lithium batteries in 'commercial' products.

10

srnet:
Depends.

What you need is some circuitry that cuts or switches off the connection to the battery.

The batteries might have an additional internal cut out, but its too low, 2.4V or so.

Far easier to use AAs as Alkaline or NiMh, do not underestimate the difficulty of using Lithium batteries in 'commercial' products.

Hi srnet,
This is what I'm using:
https://www.aliexpress.com/store/product/2S-Li-ion-18650-Lithium-Battery-Charger-Protection-Board-7-4V-Overcurrent-Overcharge-Overdischarge-Protection-4A/1829717_32754718846.html?spm=2114.10010108.1000023.5.4ad189da0UzFhK

At least it will be when they get to me...

11

OldManNoob:
Hi srnet,
This is what I'm using:
https://www.aliexpress.com/store/product/2S-Li-ion-18650-Lithium-Battery-Charger-Protection-Board-7-4V-Overcurrent-Overcharge-Overdischarge-Protection-4A/1829717_32754718846.html?spm=2114.10010108.1000023.5.4ad189da0UzFhK

At least it will be when they get to me...

A very good idea as an additional safeguard, but the cutoff will be around 2.4V.

But like I said you need to switch off your device, and in a graceful fashion, when the battery goes down to 3.0V or so.

Have you not noticed that 'commercial' devices know when the battery is low, they warn you a bit, then shut themselves down ?

How are you going to achieve that ?

12

srnet:
Have you not noticed that 'commercial' devices know when the battery is low, they warn you a bit, then shut themselves down ?

How are you going to achieve that ?

I had not gone there, but I see why that would be needed.
I will probably run a divider across an analogue input; when it reaches 3.2 (testing will determine what level to begin the process) start to flash a red led, then beep a sounder, and when it hits 3.0 flip output to another pin that's holding a SSR closed so that it opens and cuts the power. In this device the cutout need not be 'graceful' as there is no option, nor imho any need for anything but re-starting the timer setup should this occur.
Plugging in a charger will re-close the SSR and start-up will proceed.

Would you have any suggestions that might trump my method?

13

Is it essential that you run the HC12 at 115K, as that gives the least range and worst performance, as the receiver sensitivity is degraded to handle the speed.
Can you use the default of 9600 or less?

14

mauried:
Is it essential that you run the HC12 at 115K, as that gives the least range and worst performance, as the receiver sensitivity is degraded to handle the speed.
Can you use the default of 9600 or less?

Sadly, as stated elsewhere, it is a fixed speed for the driver module from Embedded Adventures - I have asked for a clarification, and what likelihood of any mod to this - and it appears to likely remain so.

I have, through tweaking the location of the HC12 module in the hand-held Tx module, and through shielding it from local interference, and by carefully choosing the aerials in use (still stubbies atm, as I cannot get my hands on any of the suggested options until after the hols), managed to get 70m without any losses. This heartens me as, with a suitable 1/4 wave or even 1/2 wave table-mounted replacement for the stubby I could conceivably extend to a very reliable 100m despite the very real likelihood of the insertion of many bodies between Tx and Rx(s).

15