Jumper T8SG - First TX stock running on Deviation

ltwvince wrote: Please share more detailed information with pictures when you have time, I would love to mod this TX to use with either 4x AA or 1x 18650. Thank you for experimenting to make this possible.

I will take some pictures, and mark up some of the pictures on the thread to make the text description easier to follow.

Actually, there is a ways to measure battery voltage against internal reference - you can measure internal reference with Vcc as reference voltage, then switch to external signal and measure it against Vcc as reference. Then you need divide latter by former and you'll have the result independent on Vcc. That's STM's recommended way as far as I understand.

Then it would not matter how precise your voltage regulator is. If time permits, I'll play with it.

ramunas wrote: I have experimented replacing the original hi-dropout voltage 3.3v and 5v linear regulators with Pololu up/down 3.3v and up 5v switching regulators on 4xAA Eneloops or 1x18650 Li-Ion battery. The goal was to keep the power shutdown and save circuitry untouched. No problems with the 4xAA in this setup (no surprise since the Walkera 7e circuitry was designed for 4xAA). With the single 18650, the Pololu regulators work well maintaining the 3.3v and 5.0v through the full range of battery voltage 4.2 - 3.0v, and therefore the system operates fine until shutdown. At shutdown the original hardware circuitry succeeds in saving model changes only for battery voltages above 3.8v. Below 3.8v there are no model change updates at shutdown regardless of the batt_critical voltage setting. Looking at the power shutdown circuitry, the 560K - 560K voltage divider at mcu pin A3 seemed to be a likely cause. As battery voltages drop below the design voltage, it is reasonable that A3 will at some point not have enough positive signal to trigger the shutdown save operation. So I reduced the 560K between A3 and J1 switch pin1 to 240K, and the shutdown save now works fine down to 2.8v. With that it seems possible to have a single 48gram Li-Ion cell provide 3000+mah. The reduced weight is nice. Note that 4 Eneloops in a Walkera battery holder are around 125grams.

I have a series of pictures to help clarify the text description above. The voltage regulators are all on the back side of the main board, so you have to disconnect enough to at least flip the board over.

There is plenty of flat space to attach the Pololu switching regulators above the stock linear regulators which I removed. I wired the Pololu's as follows:

I taped the Pololu's in the orientation shown so the wiring is clearly identifiable. The 5v step-up regulator is item #2564, and has a designation U1V10F5. The 3.3v Step-Up/Step-Down is item #2122, and has a designation S7V8F3. The Pololu's connect to 4 lands on the back of the main board as follows:

I found the removal of the stock first batch regulators took more heat than I expected, so be prepared and careful not to remove other components in the area. I left the SHDN on the 3.3v Pololu floating since the VIN already incorporates the 1-2 second power extension at shutdown for configuration saves. If your goal is just to use 4xAA Eneloops or something similar, then this is all you should need to do. A batt warning at 4.4v or so should be fine. The Pololu's will maintain the 5v and 3.3v over a battery range of 5.8v down to at least 3v, which also covers essentially the full useful range of single Li-Ion cells.

If you want to use a single cell Li-Ion there is an additional problem (failure to save configuration at shutdown for voltages below 3.8v) that needs to be cleared as discussed above. The solution that worked for me was to modify the voltage divider going to MCU pin A3:

This increases the drive to pin A3 and allows configuration save at least down to 2.8v in my unit. The location of this resistor on the main board is as follows:

A picture of my board with the parallel jumper resistor approach:

I am using this now with a batt-warning of 3.3v and a batt-critical of 2.9v. I would really plan to lower the batt-warning to 3.1v, but the Deviation user interface wont allow it to be set below 3.3v at the moment. At some point I will try to edit the Tx.ini file as a workaround, but it will take a long time for my Li-Ion cell to get down to those voltages. I just want to add that anyone trying this should continue to treat it as an experiment. I like the way it works, but until there are more users that try it out, there can easily be additional issues that may show up.

Which parts of the transmitter need 5V ?
The CPU runs 3V3 and the the RF chipsets also? Why can't we run the whole tx at 3V3 ?

Then when using a lipo or lion, can connect the cell to something as such;
www.banggood.com/5pcs-3_2V3_7V4_2V-USB-L...cts&cur_warehouse=CN

these type of circuits may also be of interest, maybe there are 3V3 out versions?

nl.aliexpress.com/item/2-in-1-Charger-Di...89d&rmStoreLevelAB=0

The red and green LEDs, buzzer, vibrater and display backlight run on the 5v rail. Much of that can be done on 3.3v with different resistors, but that is the current Jumper hardware layout. In earlier experiments, I had the 5v rail connected directly to the Li-Ion cell, and used only the 3.3v up/down regulator - all the 5v items continued to work down to 3v with a noticeable decrease in brightness or volume.

Yes, I am using the same type charger, but without the protection circuit (don't want some add-on circuit deciding when to turn off the battery when we have our own battery warning buzzer to let us decide when we want to turn off the transmitter).
www.banggood.com/TP4056-1A-Lipo-Battery-...rch&cur_warehouse=CN

What I would not do is replacing the second 3.3v LDO. There is a reason the power handled this way - two regulators instead of one. The first one is more powerful and handles the battery, but in case of switching regulator it creates noise. The second, 3.3v LDO filters this noise and provide clean 3.3v for MCU and RF chip. In Radiolink AT9 there are 3 separate 3.3v LDOs after first switching one - one for MCU, one for RF, and the third one serves only busser, because it's a collector motor and creates noise itself.

I would replace 5v regulator only to be able to handle more diverse battery setup but keep second LDO to reduce noise.

victzh wrote: What I would not do is replacing the second 3.3v LDO. There is a reason the power handled this way - two regulators instead of one. The first one is more powerful and handles the battery, but in case of switching regulator it creates noise. The second, 3.3v LDO filters this noise and provide clean 3.3v for MCU and RF chip. In Radiolink AT9 there are 3 separate 3.3v LDOs after first switching one - one for MCU, one for RF, and the third one serves only busser, because it's a collector motor and creates noise itself.

I would replace 5v regulator only to be able to handle more diverse battery setup but keep second LDO to reduce noise.

@victzh - I agree that that is the safest and most conservative way to go. And I actually experimented with something similar. Here is my sequence of experiments since purchasing a first batch T8SG. Started with a 2S LiPo and did some input voltage sweeps and saw that 5v and 3.3v linear regulators are dropping out quite early - so arrived at 7.4v as a safe batt_warning. All was good, just required frequent recharging. I wanted to improve the situation, and first experiment was to try to use the Devo 7e 4xAA Eneloop (1900mah) battery pack that fits the T8SG well. The 4xAA is in the vicinity of 5v so without removing anything I was able to bypass the 5v regulator by shorting the 5v-Vin to 5v-Vout and shorting the schottky diode between 5v-Vout and 3.3v-Vin. This worked well for 4xAA pack near full charge. But a voltage sweep showed that the stock 3.3v linear regulator had an early dropout requiring a batt_warning setting of 4.85v, and batt_critical of 4.75v. This was not really an improvement since only half the Eneloop capacity could be used. Flew that way fine for a couple of weeks, but needed to improve things for real so I ordered the lowest dropout 5v and 3.3v lin regulators of the same configuration that DigiKey had in stock.I was also looking at the following power trades:
-7.4v LiPo - hard to find more than 1600mah to fit the battery box; 60% can be used with stock regulators; 100% can be used with lowest dropout regulators; weight 120-140g
-7.2v LiIon - 3200mah available but requires some batt box surgery; only 40% can be used with stock regulators; 90% can be used with lowest dropout regulators; weight 96g
-4.8v Eneloop - 1900mah fits batt box well; cannot be used with stock regulators; 100% can be used with lowest dropout 3.3v lin regulator or Pololu up/down switching regulator; weight 125g; fairly easy recharge
-3.6v LiIon - 3200mah available but requires minor retaining slot in batt box; cannot be used with stock regulators; 95% can be used with Pololu up/down switching regulator; weight 48g; easiest recharge

So the stock regulators have to go, and I removed them. At that point, with the lands open on the main board, this seemed to be an opportune time to test the last Pololu option to get 3000+ mah, lowest batt weight, easiest recharge, and going back to the lowest dropout 3.3v lin regulator is the next step if any problems crop up. Note a comparison of the weight of a Devo 7e (534g) with 4xEneloops, and a T8SG (410g) with a 1x Li-Ion 18650:

Some of the difference is the Devo is slightly heavier anyway, but the T8SG is plenty sturdy enough. The T8SG with 4xEneloops comes in at 490g. I am aware of the possibility of noise issues with switching regulators, and was not expecting the tests to go as smoothly as they have. I have been flying Flysky, XK Futaba compatible, DSMX and DSMX 11ms protocols over the past week and nothing has caught my attention as being different from my trusty Devo 7e so far. I definitely consider this just a test or experiment at this early point. I would appreciate any suggestions of what to look for regarding a noise issue.

I personally think that switch noise are not really of an issue. The switch frequency is typically somewhere between 100khz-1.5mhz, so this will be filtered quickly by using some good coil + Multilayer caps and some additional electrolyte for buffer. The harmonics of the switcher could create some rise in noisefloor in rf bands, but I expect also not of any issue. Worst case the regulators could be metal shielded. Pololu have quite some caps present and work fine.

Nowadays all psu are switching psu. any computers but also charge adaptors etc, for me is the way to go. also more efficient for longer flytime. I avoid any traditional regulator if possible.
Could you also show the mod you did for the 7e, I manage to fit two 18650 in side, easy fit mod some of the plastic. I run the Pololu 3v3 step up down, for long time no issues. But I still run 4x eneloop as I have issue Tx not turn off if battery low...... (and as you describe, vbat must be pretty high to avoid that).

I think TX design itself is more of a risk as many quite long lanes to the CPU, are without any caps and could act like antenna and pick up RF signal cuase issues..
So f.i. using long range UHF link, could create issues, also the main tx board could have been in a shield.

Fernandez wrote: Could you also show the mod you did for the 7e, I manage to fit two 18650 in side, easy fit mod some of the plastic. I run the Pololu 3v3 step up down, for long time no issues. But I still run 4x eneloop as I have issue Tx not turn off if battery low...... (and as you describe, vbat must be pretty high to avoid that).

I never did any 18650 mods for the 7e. Maybe the previous post wasn't clear enough, but I wanted to show pics of how lightweight a T8SG with 1x18650 is as compared to a 7e with the standard 4xEneloops. The 7e has a well designed battery pack and housing, good capacity, convenient built-in charger, so I felt that was good enough. The T8SG power options need improvement, and that is what drove me to look at capacity and efficiency improvements.

Hi Ramunas ,Vlad
I instulled the aditional switches but it dosnot work and I cant see them in the transmitter manuel
Can you pleas help find what is worng in my work??
Attached photos of my wiring and ini file
Thanks

any chance any one has put a detailed step by step online, on how to add the extra switches? Would love to do it but way over my head...

Thank you it works

Most likely it means Devo 7E bootloader - early stages of development, forgot to remove the picture.

I opned new Topic “Jumper T8SG Tx 2 switches mod”
With the information l collected and photos .
I hope it can help .

your a legend, i love this community, you ask and you get cheers.

vlad_vy wrote: It's last batch T8SG. I think it related to low battery voltage. User tells he use 4xAA battery. Probably LCD low voltage lower contrast and we can see the bootloader screen instead of black screen.

Vlad, the 4xAA is the problem. I believe the last batch T8SGs are still using the same stacked 5v and 3.3v linear regulator architecture. If so, users cannot use 4xAA (nominal 4.8-5.0 volts). The 3.3v regulator is almost certainly far below regulation - and that can easily be checked. Unfortunately some vendors still advertise the T8SG as 2S LiPo or 4xAA capable which can create confusion for customers. The Jumper box and recent Bangood descriptions no longer claim 4xAA compatibility. As I recall, a month or so ago when we were coming to grips understanding that the first batch regulators were dropping out of regulation with battery just below 7volts, there was a user reporting similar start-up screen behavior.

Hello! My T8SG cannot bind with E010, is it possible to use the nrf24 multipro module to made it work?