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I have just been working on An Onboard Glow Plug Igniter for one of my planes that has a 4 stroke engine. I don't want to use fuel with Nitro, so I will need an onboard glow plug igniter. I made one, didn't fly it yet but I am sharing the project anyway.
It uses an ATtiny85 microcontroller as the heart of the device. The chip is powered by the receiver and the glow plug is powered by a 1 cell LiPo battery that I saved from an old 3s pack that had a damaged cell.
The ATtiny85 outputs PWM to the Mosfet transistors and allow to adjust the voltage to your specific glow plug.
IMPORTANT: Make sure you always start adjusting the pot with it set to the minimum (all to the left on my board), otherwise you might (should say you will) burn your plug.
You can set in the code the channel range (in microseconds) where the igniter will be ON. Default is set between 980 and 1300 microseconds. Normally ersky9x channels output 988 microseconds for minimum throttle, and 2012 microseconds on full throttle.
You have 2 lines in the code, at the beginning where you can change the values:
My board uses through hole components and SMD components, as this was what I had here.
There is an ISP header on the board so you can change the channel range settings if needeed.

Schematic:
Component Placement:
I used the mosfet IRF7425 (Datasheet Attached) because it has a very low Turn ON voltage. This is absolutely necessary.
I also used two of them in parallel so they stay cold. One might be enough but I didn't test it.
Fuses for the ATtiny85 are:
The fuses are:

Low - E2
High - DF
Extended - FF

After you programmed the fuses, you can use the arduino IDE to program the chip. You need to install the support for the ATtiny chips of course..

All files you need are attached to this post

Here is a little demonstration video.

https://www.youtube.com/watch?v=oOYssGeCgmQ

Another video of a setup intended to be installed in one of my Nitro powered planes.

https://www.youtube.com/edit?o=U&video_id=hmNHB02mrBI

I hope you like it. Comments and suggestions are very welcome. By the way, I'm not a programmer. I found pieces of code on the net, and adapted them to my needs. This includes the PWM example from the arduino IDE itself.

As always, build this at your own risk, I'm not responsible if you break or burn your (or somneone else's) nose with it, or if you cause damage to others or yourself.

João

Why use a transistor and P-channel mosfets?
When I designed one I used an N-channel mosfet (published in RC Model World in 2000).

Mike.

I had it here, it is small, it has a very low on resistance, it is rated at 15A, it has a very low ON resistance. I also use PWM so I can adjust the igniter for different glowplugs, it is not just a switch and I like to use common ground.Actually, I did think about using an optocoupler, but did quit the idea

I did look locally for a N channel Mosfet with the same characteristics, but couldn't find one. specially the low ON gate voltage.
Do you see any inconvenient in using a P Channel Mosfet apart for having to use one more component (transistor)?

Any improvement to the circuit is very welcome
Thanks

João

EDIT:

When I designed one I used an N-channel mosfet (published in RC Model World in 2000).

I probably still have that magazine in Portugal
I used to buy it back then

Hi Joao, thanks - cool little project .

I do not understand output part though. Why two MOSFETs on the output with interconnected drains and 4004 diode? Why not to use only the second MOSFET, to steer the power going to +V_OUT ?

The MOSFETs are connected in parallel. This doubles their maximum current and halves their internal resistance. In other words, they will not get so hot, that is the idea.

Also, don't forget that if you replace the glow plug with a different one, you should calibrate it again by turning the trimmer to the OFF position and start from there, otherwise you could kill the new plug.

João

Thanks Joao, all clear now .

What current does it actually take? let's say for OS no. 8 plug?

I think I will skip the potentiometer and calibrate the output permanently for 1.5V ... maybe even in the hardware, using some linear voltage stabilizer (if the current is not too high).

I never measured the current or voltage. Just adjusted the trimmer for the best glowing setting. You can just do that and then leave the trimmer alone. If you use the same type glow plugs you don't need to change the setting then.

And it is not a potentiometer, it is a trimmer. It is small

João

I'll check the current on one of my commercial glow drivers. With linear voltage regulator I could power it from the on board battery and not being dependent on its level...

Anyhow - thanks again for the overall concept!

Ok, my circuit works with PWM generated by the microcontroller. I believe it could still be improved, but it works well, so I didn't bother

João

Sent from my BLN-L21 using Tapatalk

Seems it works great mate. I just don't need to regulate the voltage and want to power it from 2S rx pack, keeping consistent 1.5V to drive the plug.

Never tried 2S..

João

Sent from my BLN-L21 using Tapatalk

Should work, why not, just different PWM to steer MOSFETs or linear regulator and MOSFETs just as a on/off switch.

I think it is not that easy, you would need a linear regulator that could handle at least a few Amperes and dissipate a lot of heat.
Even if you find such a regulator, you would need a huge heatsink on it. This would make the complete assembly very big. The way to do it is to build it with a MOSFET. Now you made me curious to know if my circuit/code could be changed to make it work with a higher voltage power supply.

João

Sent from my BLN-L21 using Tapatalk

That is why I asked about current at the beginning... if it is too high for a regulator, PWM steering MOSFETs will do the job .

For that you just need a normal glow plug driver circuit that can be found on the net, and some kind of RC switch

João

Sent from my BLN-L21 using Tapatalk

jhsa wrote: ↑Tue Feb 26, 2019 11:23 am For that you just need a normal glow plug driver circuit that can be found on the net, and some kind of RC switch

Right, just I want to have it on one nice and compact PCB .

I checked one of my commercial glow drivers Joao. It starts with 6A, to get to 4A in around 3sec and then it is steady at this level until switched off.

I still didn't understand what you want to do It looks like you just want a normal glow plug driver that you don't have to adjust, just like the one I built but without the trimpot. But I believe the commercial ones also need adjustment for the right type of plug??

João

All plugs I know runs on 1.5V ... And this is how most traditional glow drivers work, it is basically simple NiMh cell.

https://www.amainhobbies.com/dynamite-m ... 00/p474340

Such a thing has no electronics inside. The cell is connected directly to output terminals.

But some plugs draw more current than the others. some will glow brighter than others.. With that glow driver you cannot fine adjust how bright they glow. Current matters more than voltage in this case
You could of course get one of those batteries and install it inside the model with an RC switch.. But it would be heavier than my solution. As I said, I don't really understand what you are trying to achieve To make this work (without a huge heavy battery you need some circuit like the glow starters used on the flight boxes, from a 12V battery. It is usually an oscillator and a power Mosfet, and you can adjust the current with a potentiometer.
The reason I made mine work with one LiPo cell is that I wanted it to be powered separately from the receiver battery, One cell is quite light weight, and I can savage it from a damaged flight pack. So it is also cheap
My PCB is also not so big considering that I also have a voltage sensor for measuring the glow battery voltage. Ok, if I used an SMD ATtiny85 and removed the ISP programmer plug, it could be made even smaller..

João

I'm not challenging your design . Opposite actually, it was a good inspiration, in fact almost ready to use .

What I want is to have it powered from 2S, not 1S, as I actually want to use RX pack, to avoid hassle with dedicated 1S battery. I was also wondering if I can make it without MOSFETs and PWM control. But it will be difficult if we are talking 6A range, unless I want to use a relay.

Is it the current what really matters in this application? In these very simple NiMh drivers you have battery directly connected to the plug. There is no current control there. The plug takes what it wants, or rather what its resistance is. Thus I do not see a need for regulated voltage / current control.

Seems what I need is step down from 2S to 1.5V and on/off switch with a 30s timer .

rcyoda wrote: ↑Mon Mar 04, 2019 11:17 am What I want is to have it powered from 2S, not 1S, as I actually want to use RX pack, to avoid hassle with dedicated 1S battery. I was also wondering if I can make it without MOSFETs and PWM control.

Well no since the MOSFET and PWM are what allows reducing the voltage from the 2s battery. If you just had your 2s and a relay you'd jsut blow the plug instantly...

Kilrah wrote: ↑Mon Mar 04, 2019 11:28 am Well no since the MOSFET and PWM are what allows reducing the voltage from the 2s battery. If you just had your 2s and a relay you'd jsut blow the plug instantly...

Clear. That's why I wrote that I need a step-down from 2S to 1.5V ... and then on/off switch.

I'm still wondering though about that "current matters". As I can see it, it is not, as long as you keep standard 1.5V drive. Current will regulate itself, just by a resistance of the plug. Am I right?

As I said, this is not about voltage, it is about current..

João

jhsa wrote: ↑Mon Mar 04, 2019 11:58 am As I said, this is not about voltage, it is about current..

Hm, in that case seems do not understand your diagram fully. And I though it is a simple one .

With PWM what do you regulate, current or voltage? I thought it is nothing else as switching voltage regulator?

It's current that matters, but since we're dealing with a resistor it's all same thing.
You adjust the voltage with the pot but by looking at getting the right current...

Kilrah wrote:It's current that matters, but since we're dealing with a resistor it's all same thing.
You adjust the voltage with the pot but by looking at getting the right current...

Ok, I think I got you guys now. You are talking in general. Yes, in general it is current which matters and can blow the plug. Still you regulate the voltage though.

So back to specifics of the design. I think I will be actually measuring input voltage, adjusting the PWM to get always stable 1.5V on the output (no matter what current RX voltage is) and do not care about the current, as it cannot blow the glow plug if I keep 1.5V.

Actually I googled a bit and cannot find any plugs which require different voltage than 1.5V. I reckon output voltage regulation is simply not required and not practical. Did not spent too much time searching though. Maybe there are some special kind of glow plugs, which I don't know.

Please google "Ohms law".. Voltage, current and resistance are all related.
Those starters with one single battery are less than ideal for some type of glowplugs, at least as my experience is concerned. that is why I built one for my flight box.
And looking at the Amperimeter on my flight box glowplug driver, different plugs achieve the same brightness as different current settings. This makes the adjustable driver much better than the other with just a battery inside.

a stepdown converter from 7V might work, but you will have to get one where you can adjust the voltage (and therefore the plug current). So, this will do exactly the same as my circuit, only with a 2 cell battery. You could build an RC switch that will switch the adjustable converter, but that will make the whole thing 3 times bigger than the circuit I built.

And by the way, I never thought you were challenging my design. It is what it is, certainly not perfect, but it works for me

João

Sure it works Joao, for you and not only . As I wrote I it is also almost ready to be used for my application. I will just skip output regulation part and focus on getting stable 1.5V there. I never had any issues with these simple one cell drivers. They always worked for me, just it is pain in the a** to plug them every time you want to start a motor...

rcyoda wrote: ↑Mon Mar 04, 2019 12:41 pm

Ok, I think I got you guys now. You are talking in general. Yes, in general it is current which matters and can blow the plug. Still you regulate the voltage though.

yes, you adjust the PWM and hence the voltage to control the current. They are proportional.

So back to specifics of the design. I think I will be actually measuring input voltage, adjusting the PWM to get always stable 1.5V on the output (no matter what current RX voltage is) and do not care about the current, as it cannot blow the glow plug if I keep 1.5V.

Stable 1.5V might work for some plugs, or might not. It depends on what current the battery can supply as well..

Actually I googled a bit and cannot find any plugs which require different voltage than 1.5V. I reckon output voltage regulation is simply not required and not practical. Did not spent too much time searching though. Maybe there are some special kind of glow plugs, which I don't know.

I think I have seen plugs for 2V in the past. But that doesn't matter as it is just a reference for people that don't understand how electricity works what makes the plug glow is the current passing through it. But feel free to test the converter to 1.5V and see how it works.

João