38 replies to this topic

[Kermet]

Hi, just wanted to know what guys have made up for there voltage reg for the Airwave 633 tx

Cheers
Brett

[Thorn3]

Brett,

I personally have not used or experimented with this module, so I do not know how sensitive its input voltage requirement is. I looked at the documentation for the Tx and it did not indicate a voltage input range. Due to this, I would assume they mean the input should be precisely 3.3 VDC. If this is truly the case, then you could easily use an LM317T, adjustable output, linear voltage regulator. Use a pot when setting up the regulator circuit and adjust to exactly 3.3 volts. Either use a dab of adhesive to hold the pot at value after adjustment, or replace the pot with a permanent value resistor. I am assuming that like the Tx module, you will be using all SMD components? This is why I suggest a linear regulator chip, such as the LM317T. It is available in SMD form (as is the pot, etc) and will integrate into your PCB easily. Be sure to use a supply voltage to the regulator chip, that is at least 3 VDC higher, than the expected output voltage. In this application, it would appear that at least 6-9VDC in, would suffice. I do not prefer the use of linear regulators generally. Typically, when possible, I would use a switch mode. Dimension Engineering (dimensionengineering.com) has adjustable output switch mode supplies. They are reasonable in price and just might be what you are looking for. Switch modes are more efficient than linear supplies, although larger and more complex. The smaller ones are not much larger than a linear regulator in a T0 220 housing.

Robert

Hi, just wanted to know what guys have made up for there voltage reg for the Airwave 633 tx

Cheers
Brett

[Terry]

Try a search on this forum, this has come up before. I seem to remember someone used diodes to drop the voltage as it was not critical.

Terry

[Kermet]

Thanks Robert and Terry,
yes sometimes we make things harder than they need to be and the 317 is simple, I just had to
ask just in case there was some other preference the 633 had,

terry I did a search before posting and could not find what i needed,i want to use my 1200ma 3s, but i have a dpc-171 camera,mic,633 Tx,regulator and Rc Rx to power up from same supply. just thinking of it sounds like there be power wires going everywhere......

Rob, it will not be SMD as i have another job for it first ( security )

Cheers
brett

[Mr.RC-Cam]

A linear Vreg will run seriously hot on a 3S setup. To avoid that, I used the Dimension Engineering 3.3V Vreg when I built a AWM633 rig. But the DE Vreg had a lot of switching noise that caused lines in the video. I had to add inductors and caps to the input and output of the Vreg to eliminate the noise artifacts.

[Thorn3]

I also prefer the switch modes. All of my FPV aircraft use switch mode supplies. My camera uses 5 VDC, the mic with built in pre-amp uses up to 12 and so does the 500mW video Tx. So, my switch mode is used on the camera only. I use a separate battery for the camera system (camera, mic and Tx). It is an 800mAh LiPo, 3 cell (good for four flights). The aircraft uses a 1500mAh 3 cell. Funny that the two batteries weigh the same as one 2200mAh battery. A good balance. I don't have any lines of interference. Although I have seen this when people use the same battery used to power the other functions of the aircraft ie: motor, ESC etc., for their camera system, or the regulator was within close proximity to other devices. I (presently) place my switch mode relatively far aft in the aircraft, to avoid any EM fields that could be picked up by any servo, camera or other lines. Otherwise, surely as MR.RC-Cam put it, filter it out if need be.

I was going to post earlier, after the diode suggestion, that if a one cell were being used, then a simple diode voltage drop would be appropriate (only .4 volts drop needed). But, no mention was made as to the other components (at that time) in the video system and their power requirements, nor the main supply voltage, so I did not comment.

But... there may be hope soon gentlemen. My partner and I are finalizing a new switch mode regulator series. Efficiency is presently 95%. These supplies are being designed specifically for RC use. They do not induce the same issues into RC aircraft electrical systems like older designs do. I will post when and where they will be available. They are presently in the field testing stage. I have to abuse a few of them in some of my own aircraft for a while first.

[robmitch]

Just to add the the questions, I will run camera/vtx from a 2s battery, so I think a linear reg will be fine. I was goint to use a tlv1117 fixed 3.3V reg. My question is placement:

I want to make the transmitter as small as possible, so I can use it on smaller planes, but more importantly, I want to mount it at the very wing tip/tail, so weight/size is important to me. Electrically, for the transmitter module, it makes sense to have the regulator on the module pcb, but any opinions of whether it will be a bad idea to make a separate regulator pcb in the fuselage and a have a 3.3v supply wire going to the vtx?

[Thorn3]

If you are going to use a fixed, linear regulator, it could be in either an SMD or To220 case style. Either one, can be hard wired directly to the pins. Since it is a fixed regulator, you would not need a PCB for it, as no support components would be needed, unless you want to thread the power lines through something like a ferrite, toroidal core, to reduce power spikes. Filtering with .1 to .01mF capacitors would typically be needed if the power lines are 6" or longer. A simple heat sink on the regulator is all you need. No PCB. Just shrink wrap over the pin/wire connections. You would not have to put the regulator directly on the Tx board. I don't. I use a switch mode, but hard wire to the pins instead of doing an on-board regulator. Power wires run out to the video Tx. Works well, with no interference.

[Kilrah]

2s to 3.3V @ 600mA with a linear reg will get very hot as well (nearly 3W dissipation!). You'll need a beefy heatsink, so if you want to keep the TX itself light then yes I'd recommend a separate location for the regulator.

[Thorn3]

Certainly use a heat sink. I live in the desert, where it is hot much of the time. The difference between ambient air temperature and ESC's or video Tx's temperature, isn't much. Thermal transfer is more difficult as a result. In the picture, you can see a simple, GWS Texan foamie(1/12 scale, parkflier) outfitted with a pan and tilt camera and 500mW video Tx. You can see that my ESC is in the outer wall of the fuselage. The video Tx, is mounted behind the second seat, but also outside the fuselage. This is to allow the greatest amount of airflow over them. They are both heat-sunk of course. The camera gets fairly warm and the video tx gets quite hot. Due to this and the need for airflow to keep things cool, there is no glass in the canopy. It was built to replace the original vacuum formed canopy, but is a framework only (laminated Birch veneer).

In my two 1/12 scale P-51 Mustangs (full balsa builds) I take advantage of the chin intake and the oil cooler intake (under wing scoop) to keep things cool. ESC at the chin intake and the video TX inside the oil cooler intake duct. Air is free to flow into the chin intake and the oil cooler intake. All air is free to flow through the fuselage and out the oil cooler exhaust hatch. Funny that ESC companies always say to locate the ESC in an active airflow for them to run properly, yet most people bury them in stagnant air inside the fuselage. In my case, here in the desert, I cannot get away with that. So heat sinks and airflow in any clever way that can be found.

To avoid the need to purchase heat sinks, I typically use ones found in other devices. However, if the need arises, there is no reason not to machine my own from aluminum. The ESC heat sink is originally from a 2.4GHz @ 500mW video Tx. Since I use 900Mhz video, no need to keep a perfectly good heat sink on a video Tx that I do not use. The heat sink on the video Tx is actually an old computer processor heat sink. I cut it down, to fit the width of the video Tx. Since my video Tx is housed in an aluminum case (Range Video Tx), I was able to remove the top and screw up into the heat sink to secure it to the Tx housing. Of course, use thermal transfer compound or pads, such as those used as thermal isolators on common TO-220 transistors and other devices in such housings.

For my camera, I have to drop the 11.1 battery down to 5 VDC. My regulator is switch mode and it does not even use a heat sink, nor is it located outside of the fuselage. It barely gets warm to the touch. The camera does not draw nearly the current of a 500mW video Tx. But, since you are going with a linear regulator, expect some heat. A TO-220 case style linear regulator is good typically for up to 1.5 A, when heat sunk. So, you will be drawing approximately half of the regulators capacity. If you locate your heat sink in an airflow, you can use the smaller, lighter heat sinks for TO-220 type devices.

Sorry for the low image quality. This forum does not allow for large file sizes.

[Mr.RC-Cam]

Besides the heatsink, be sure to add the stability caps recommended on the Vreg's data sheet. Do not omit them.

[robmitch]

Right,
slight change of plan. I will now use 3s main flight battery... Use separate switching bec at 5v - 5A for receiver and 5v camera, and then drop that 5v down to 3.3v with the LDO reg on the tx module (with lots of filter caps). Can I get away with 6.3v 470uF tantalum caps for the tx module, or even 4V (these are on the output side of the 3.3v reg). I can get 10v ones, but much more expensive...

[robmitch]

Having done a bit more reading, it looks like i will be asking for trouble if I have V/Vmax > 50%. I will stick to the 10V caps - that way I will have just over 30%, and reliability.

[Kermet]

i just received my 633 TX modules and but found this interesting low drop out regulators, LM3940 which is a 3.5 volt 1 amp and wonder
if this will do the job for the 633 ....also with the 633 do all the earth pins need to go to earth (GND) as one wire or are they just
showing they are internal connected to earth ?

Plus with the channel 1,2,3 do they get wired to earth for there individual selection ?

(i keep adding questions while you are all asleep)

Also what is the best capacitors to use on the TX, can i use electrolytics if i havent got the ceramics that i guess you guys may recommend ???

thanks
brett

Edited by Kermet, 05 November 2009 - 11:24 PM.

[Thorn3]

Any pins showed to be wired external to the block diagram of the component, are grounded to a common ground plane, or trace, to the negative terminal of the supply. They are not internally grounded.

Here is their text regarding channels:

"Channel selection is four channel and default value is ch4 (not enable). Other channel can be selected by pulling low to enable".

I understand this as meaning that channel 4 is default selected (enabled internally) and pulling any other channel pin to ground will select that channel. Switches such as PCB DIP switches would be nice, or jumpers so you can select any channel at any time, without having to solder or unsolder the pins to change channels. If you fly FPV with other pilots, the ability to change channels in the field is very important.

470uF is a pretty high value, at 16 and 25 volts, so I don't know if you can get them in ceramic or Tantalum.

I don't want to insult anyone, but I am curious. Why are people using the 633? A circuit has to be built, it uses a specific, low voltage input, resulting in only about 500 feet of line of sight range -AT-500mW. Seems like an awful lot of trouble, when there are video/audio Tx's out there that are plug and play, use a range of input voltages from about 7-12 volts and have a range of several miles/kilometers and they cost less than the 633. Is it a license issue?

[Kilrah]

resulting in only about 500 feet of line of sight range -AT-500mW.

Huh? It gets the same range as any other 500mW TX...

[Mr.RC-Cam]

what is the best capacitors to use on the TX, can i use electrolytics if i havent got the ceramics that i guess you guys may recommend ???

Generally speaking in these applications, the small values are ceramic. Large cap values ( perhaps >1uF) are usually high quality electrolytic or Tantalum. It helps to have some RF experience if you will be using any RF module since many of the requirements for best operation are up to the designer.

I don't want to insult anyone, but I am curious. Why are people using the 633? A circuit has to be built ...

Not insulted, but a bit surprised. This is a DiY web site dedicated to wireless video and other interesting projects. Folks that buy ready-to-use solutions would probably not be interested in coming here.

... resulting in only about 500 feet of line of sight range -AT-500mW

As Kilrah stated, its 500mW range is exactly the same as any other good performing 500mW 2.4Ghz Tx. Some "500mW" Tx's demonstrate much lower RF power than advertised, so with a proper RF implementation the Airwave can even be better than the ones that cheat with their specs.

Edited by Mr.RC-Cam, 05 November 2009 - 11:00 AM.
Added info on caps

[Kermet]

Hi Thorn3, i just went for the 633 as it has the most power....for a diy price....(im not flying with this system)But if you know of better/other options please share them as id been keen to look at all there is that will help

So what do you think of the LM3904 ??? is 3.5 volts ok for the 633 ?

brett

[Thorn3]

Hi Thorn3, i just went for the 633 as it has the most power....for a diy price....(im not flying with this system)But if you know of better/other options please share them as id been keen to look at all there is that will help

So what do you think of the LM3904 ??? is 3.5 volts ok for the 633 ?

brett

I have not used the 633. I have only read its data sheet. I would assume that 3.5 volts would not damage it at all. If it is like most other modules. There is typically some flexibility.

I know this is a DIY site. I only suggested the available RF transmitters, such as the Range Video Tx's, because RF can be complex if someone isn't well versed in it or feels uncomfortable building one. All video Tx's that I have used and read about, state that input voltage is a function of range. So, even my 500mW Tx will be greatly diminished in range, if I use a lower input voltage. Since I am not familiar with the actual use or architecture of the 633, it confuses me why 'that' module is different from all others, in its ability to transmit long range at only 3.3 volts, without the use of a broadband amplifier on its RF output stage. Unless it has a built in broadband amplifier, but then the data sheet would not claim a range of only 500' and say that it doesn't require a license to use, due to its low output. Video Tx's with an output of 250mW and above, require a license. Although, I have yet to meet anyone that actually has a license to use them. But, since the 633 is sold under the statement that it does not need a license to operate it, I lean towards believing that it really is a low power, short range Tx. If anyone has technical documentation to show otherwise, I would like to see it. This is not a challenge to anyone's success with the 633, simply technical curiosity.

I believe heavily in a DIY environment. Most of what I do is DIY. But to me, an existing RF transmitter is a building block, just like any other block, such as a camera, battery, voltage regulator or IC's. Putting the whole system together, to me, is DIY, be they discrete components, or a combination of blocks and discrete components. This is because you still have to deal with power regulation, wiring, filtering etc. With the video Tx I suggested for your project, you would not need to regulate the voltage to it. You could power it straight off a 3 cell. The price is less as well. But, you would have to regulate power to your camera and devise filtering on the signal and power lines. It is still a DIY if you use an available Tx. Just another building block in your DIY system. If building a DIY Tx is your goal, then certainly go with the 633. If you find the range is not suitable, then simply add a broadband amplifier to the RF output stage and you will see a dramatic increase in range.

I am familiar with the National Semiconductor LM3940 voltage regulator. I believe it would be good in your application, regarding the 633. (the LM3904 is a transistor : )) Even though the LM3940 claims it does not need a heat sink, I would use at least a small one anyway (I don't know the working environment), unless you are going to design a PCB and use a surface mount package, so you can solder it down to a copper plane for heat sinking. But, this will increase your PCB footprint. Always believe something will overheat as a general rule. Ambient temperature can have adverse affects on thermal transfer. You will be potentially using more than 50% of the total capacity of the LM3940. Typically, if something such as a voltage regulator overheats for any reason, it will go into thermal shut-down and you will lose your power.

[Mr.RC-Cam]

Since I am not familiar with the actual use or architecture of the 633, it confuses me why 'that' module is different from all others, in its ability to transmit long range at only 3.3 volts,

The Airwave modules are highly integrated RF components and are capable of driving their rated RF power at the specified supply voltage. Even the 3.3VDC powered AWM633TX.

the data sheet would not claim a range of only 500' and say that it doesn't require a license to use, due to its low output.

Airwave's 500 foot range description is a bit too conservative (add another zero). Regarding not needing a license, I think there is some confusion about that. Some of their Tx related data sheets indeed mention "Conform with R&TTE & FCC stipulation" but that is only if you use their 0dBm (<1mW) rated module in USA applications or the 10dBm (<10mW) module in CE territories. However, there are still other technical/legal considerations that need to be met before license free use would be granted.

For that reason, these modules are well suited for licensed hams that can legally operate them if they follow the amateur radio rules. The license issue is the same for all the popular FPV systems used in the USA and perhaps many other countries (it's not just an Airwave issue).

If building a DIY Tx is your goal, then certainly go with the 633.

I agree. Every RF engineer I know had to start somewhere. They became good designers by building, experimenting, and learning from their RF mistakes.

The Airwave modules sort of let you cheat since most of the hard stuff is already done for you. But, since there is more to them than plugging in a cable and applying power, there's a lot more to be learned. The long standing members on this forum have traveled this route in their early attempts and the wisdom they often share usually reflects the school of hard knocks. So, I am impressed with anyone that rolls his own using an Airwave module. They are usually the ones that will be back to help the guys with their store bought stuff.

is 3.5 volts ok for the 633 ?

I cast my vote to 3.3VDC ±2%.