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Member postings for Mike Blandford

Here is a list of all the postings Mike Blandford has made in our forums. Click on a thread name to jump to the thread.

Thread: Build your own telemetry sensors.
21/05/2019 19:56:22

David: A bit of confusion, the A3 and A4 here are the FrSky telemetry values being sent, not the A3 and A4 analog inputs to the Arduino.

Chris has solved the problem by setting a scaling value of 0.1 in the configuration file (discussed on another forum).

Mike

20/05/2019 14:51:59

Just change the MVOLT_AT_ZERO_AMP value to 1650:

#define MVOLT_AT_ZERO_AMP 1650 // in millivolt

and you should get a correct 0 Amp result.

Mike

19/05/2019 20:52:21

Andy: It looks to me that you have the pack voltage and the current swapped over in your config files. 47A looks to be what you would get if using 12.2 volts on the voltage input and using the measured value as the current.

Mike

19/05/2019 19:32:56

The output of the current sensor is "ratiometric" to the supply voltage. The value of 40 (mV per Amp) only applies to a supply voltage of 5V. At 3.3V supply, the value is 26.4 mV per Amp ( 40 *3.3 / 5 ).

Mike

18/05/2019 16:31:54

In oXs_config_basic.h I have (comments removed):

#define VFAS_SOURCE VOLT_6

In oXs_config_advanced.h I have (comments removed):

#define REFERENCE_VOLTAGE 3300

// ***** 6.2 - Voltage parameters *****
#define PIN_VOLTAGE 0 , 1 , 2 , 6 , 8 , 7
#define RESISTOR_TO_GROUND 2.70 , 2.70 , 2.70 , 2.70 , 0 , 2.7
#define RESISTOR_TO_VOLTAGE 1 , 4.7 , 10 , 12 , 0 , 18
#define OFFSET_VOLTAGE 0 , 0 , 0 , 0 , 0 , 0
#define SCALE_VOLTAGE 1.00 , 1.0 , 1.0 , 1.0 , 1.0 , 1.0

// ***** 6.5 - Current parameters *****
#define PIN_CURRENTSENSOR 3
#define MVOLT_AT_ZERO_AMP 344 // in millivolt
#define MVOLT_PER_AMP 26.35 // in milliVolt per Amp
#define RESISTOR_TO_GROUND_FOR_CURRENT 0
#define RESISTOR_TO_CURRENT_SENSOR 0

The MVOLT_AT_ZERO_AMP value is first from measurement, then adjusted to give 0.0A (I had -0.3 to start with!).
The MVOLT_PER_AMP value comes from 40 / 5 * 3.293 as I measured VCC at 3.293 volts.

Mike

16/05/2019 23:24:05

I have one of these working on pack voltage, current and cell voltage (3S tested so far), using your second revision board. Some observations:

1. The ground tracks a quite thin. I would normally use 50 thou width for ground, or create a ground plane.
2. The holes for the resistor leads are larger than needed, I would normally use 0.8mm for these and 1.0mm for (square) header pins.

You have a ground wire connection from the main power negative connecting to the board for measuring the flight pack voltage.This can create two ground paths to the ESC. One is along the main power connection, the other is via this connection to the board, through the board, along the ground of the SPort connection to the Rx, through the Rx and along the ground connection of the throttle connection to the BEC of the ESC.
The main power connection will be a very low resistance, although the power connectors (4mm gold shown) may add a few milliohms.

Now I'm guessing a bit on these values but suppose the main power connection is 5 milliohms and the other route through the board and receiver is 200 milliohms (0.2 ohms). The motor current will split between these two paths in a ratio of 200 to 5 (40 to 1). So if your motor is taking 41 Amps, 40 goes along the main connection but 1 Amp will go through the receiver and board.

I would suggest the wire from the LiPo negative to the board is not fitted.

I'll be adding my pressure sensor, although my board is a few years old and has a different arrangement for the connections. As have been testing using a G-RX8 receiver (to a X9Lite using the new ACCESS protocol) I had altitude anyway!

Mike

Thread: FrSky Neuron ESC
16/05/2019 15:56:18

Yes, but the FUC-1 outputs inverted serial while the FTDI is non-inverted. The diode is polarised the "other" way round. I did think could we use a FUC-1 then remembered it was inverted!

This is the same principle.

Mike

16/05/2019 14:11:29

Testing a FrSky Neuron ESC. You need to use BlHeli_32 on your PC to configure it. The BlHeli program offers several ways to connect. I originally used an Arduino nano, flashing the nano from the BlHeli program.

I have also used an Arduino Pro Mini, connected to the PC using a FTDI type device. I just "told" BlHeli it was a nano an flashed the Arduino then used it like the nano.

Having looked at what the Arduino was doing I came up with this. You just need a FTDI type device, a diode and a resistor. I just tested it and it works fine.

Mike

neuron.jpg

Thread: Build your own telemetry sensors.
09/05/2019 00:11:00

The '328 datasheet shows the internal bandgap reference is between 1.0 and 1.2V, with a typical value of 1.1V.

One way of using this is to use VCC as the reference voltage, but then use the ADC to measure the bandgap voltage, This enables you to work out what the VCC value is and detect if it is lower than expected.

I use this method in er9x for the 9X radio where if the radio battery drops too low, the VCC drops and the actual measured battery voltage appears to increase.

Mike

07/05/2019 23:12:44

The maximum operating frequency of a MEGA328 changes linearly from 10MHz at 2.7V to 20MHz at 4.5V. 16MHz therefore needs just under 3.8V, so works fine at 4.8V.

Mike

07/05/2019 18:50:34

Be aware that the maximum guaranteed clock speed when operating at 3.3V is 13.333MHz. 16MHz is not guaranteed to work across all devices and temperatures.

There is an option on the MEGA328 to divide the oscillator frequency by 2, and it is recommended to use this in the application firmware if running a 16MHz crystal with a supply of 3.3V.

Mike

Thread: Jumper T16
29/04/2019 13:02:00

Yes, I believe all the modules are based on the DIY multiprotocol module, they all run the firmware as available on Github. Jumper did have the wrong chip on the module shipped with the T12. That chip controlled the inversion of the serial data to/from the module, but they should have fixed that.

Mike

28/04/2019 22:23:02

BTW, the firmware on the multiprotocol module is open source, it is NOT a Jumper development (any more than the firmware on the T12 and T16 has any real development done by Jumper).

This is part of the reason why the Jumper hardware is lower cost.

The firmware for the module is here: **LINK**

Pascal maintains this, and has done much of the development. If you use the multiprotocol module please consider making a donation to Pascal for all the work he has done (donate buttons on the page in the link above).

Mike

28/04/2019 21:52:21

Details here: **LINK**

Yes, with the diode, it does work in a Taranis.

Mike

28/04/2019 17:56:31

Try using a different "receiver number" on the Tx. I know, with the S6R/S8R there is a problem with some XJT modules with some "receiver numbers". I suspect it has to do with the module unique ID. Yo may have a similar problem with the 4-in-1 module.

If you are using an unmodified DJT module then the telemetry data is only available on the connector on the rear of the module.I have modified my DJT modules so the telemetry signal connects to the bottom pin of the module connector (via a resistor and with a diode clamp) so the telemetry is available directly.

Mike

28/04/2019 00:03:35

The "FrSkyX" LBT protocol in the 4-in-1 multiprotocol firmware doesn't actually do a listen, it just handles the correct data format. I'm not aware of any plans to fix this (and I coded the changes to support the LBT option).

On all the multiprotocol modules I have, I notice the power output when using the CC2500 chip (used by FrSky protocols) is noticeably lower than a "proper" FrSky module. Careful range checking is therefore recommended.

Personally, I only use real FrSky Tx modules for the FrSky protocols because of this.

Note that FrSky are also very unhappy with Jumper as Jumper appear to have basically copied the FrSky X7 (for the T12) and the X10 (for the T16), so taking advantage of all the development work done by FrSky without incurring the corresponding costs.

FrSky provide me with technical data on their radios (under a NDA), to enable me to port ersky9x firmware. I've been waiting over 5 weeks for similar data for the T16!

Mike

Thread: Build your own telemetry sensors.
23/04/2019 15:58:55

Just for information, the lower of those two boards matches the "official" Arduino Pro Mini, as seen on the Arduino site. I also note on the rduino site it indicates the Pro Mini has been "Retired"!

Mike

Thread: Understanding the numbers....
21/04/2019 01:27:18

Even with the model on the ground, the height of the aerial above the ground is important. The range you get could be significantly different if the aerial(s) are at the bottom of the fuselage or at the top. You could easily by looking at 4 inches or 6 inches, which would make a 50% difference to the range!

Mike

20/04/2019 21:46:46

A couple of things (if you are measuring accurately). 90 feet is 27.4 metres. Going 30 metres away is 10% further.
Secondly, and more significant, the range you get is proportional to the height of the receiver aerial above the ground. Depending on where on the model the aerials are, they could be very close to the ground, e.g., on a glider with no undercarriage they could be only 3 inches off the ground, on a power model with an undercarriage, they could be 6 inches above the ground. You would get a significant increase in range with this.

I always do my range checks with the model on top of my flight box, so the aerial height above the ground is about the same for all models, probably about 12 inches.

Also, in your back garden, you may be getting signal reflections that cause the range to be reduced.

Mike

Thread: Build your own telemetry sensors.
17/04/2019 19:32:20

Andy: When adding heatshrink, make sure you don't block the holes in the pressure sensor.

If you just want to sense analog voltages, I have a simple project here (uses 3.3V, 8MHZ Arduino): **LINK**.

Looks like I built my vario sensor back in December 2015, after I had written the code for the SPort interface and the millis()/micros() that work without using interrupts so the software serial timing works reliably.

Mike

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