Dangerous Prototypes Open Source Hardware

Transmission distance is very short?

August 31, 2010, 02:06:43 am

Hi, all~
The IR toy works well now in my computer, I capture the IR signal and replay it to the target device. But it seems the transmission distance is very very short (about 15cm..) and the valid angle is very narrow (about 10 degree)..

How could I improve the transmission distance?

Thanks.

Re: Transmission distance is very short?

Reply #1 – August 31, 2010, 02:41:26 am

Take a look at the schematic, and calculate the current that should flow in the IR LED.  Then check the specifications for the IR LED and see what the maximum might be (25 mA constant, more if pulsed?).  Also check the maximum current that can be supplied by the transistor (800 mA?).

You might be able to change the resistor in increase the brightness of the IR LED.  I think that different revisions of the IRToy had different resistors.  If you scan through the IRToy sections of the Dangerous Prototypes site and forum, you might find mention of changes to the resistor.

Re: Transmission distance is very short?

Reply #2 – August 31, 2010, 11:08:53 am

I found that as well with the transmitter. That's why I thought it might be using the wrong frequency.

Re: Transmission distance is very short?

Reply #3 – September 01, 2010, 11:28:31 am

Dukey I believe has the latest version with the 180ohm IR LED resistor for 20mA of current.

@diro - can you make out anything on resistor R4? Ideally it will read 1800 (180ohms), though it might be bigger giving lower current if it is from an early batch. If you have the smaller LED, you can send it to me and I will replace it.

The distance can be increased by upping the current to the maximum supported by the LED. It is pulsed, so most have a 100mA or so rating when used for short remote control bursts.

You can remove R4 and replace it with a smaller resistor, or add a second resistor on top of R4 to increase the current supplied to the LED.

With the transmit function being better supported, we're probably going to see a number of short-comings of the single-LED design. It's probably a good time to study up on the TV B Gone and similar for a more powerful approach.

Re: Transmission distance is very short?

Reply #4 – September 01, 2010, 12:49:02 pm

[quote author="ian"]The distance can be increased by upping the current to the maximum supported by the LED. It is pulsed, so most have a 100mA or so rating when used for short remote control bursts.[/quote]Unlike most visible LED ratings, IR LED specifications indicate higher current capacities.

The shipping IRToy uses the TSAL5300, which can handle 100 mA continuous, 200 mA peak, and 1.5 A surge.  Those are absolute maximums, but the charts only seem to show up to 1 A.  They don't seem to precisely define "surge" versus "peak" though.  You could drop R4 to 39 Ω or perhaps even 19.5 Ω.  According to Fig. 3 in the data sheet, it would seem safe to use 200 mA with any pulse duration in the displayed range, so long as the duty cycle is 50%, but you'll want to double-check that the PWM frequency is within the tested range on the chart.  If 200 mA doesn't provide enough range, the chart shows the 10% duty cycle could handle anywhere from 300 mA to 700 mA, depending upon the pulse duration, i.e., depending upon the PWM frequency.  You also want to check the forward voltage, because it increases as current increases, so your R4 calculations will shift as you boost the range.

The preorder 1 IRToy (which I have) has the SFH-480 IR LED, whose specifications seem to indicate that it can handle 200 mA continuous, and as much as a 2.5 A surge!  At 200 mA, the forward voltage is around 1.6 V, but it increases with more current, to as much as 3.7 V at 2.5 A.  I did not immediately notice any specifications as to how short the pulse must be for the surge.  In other words, if you have the preorder 1 IRToy with the original SFH 480, then you should be able to increase the current to 10x !  i.e. change from 180Ω to 18Ω.

No warranty: so beware that you don't let the magic smoke out.

Re: Transmission distance is very short?

Reply #5 – September 01, 2010, 06:35:12 pm

If there are any improvements to the IR LED, will v1.1 have them?

Re: Transmission distance is very short?

Reply #6 – September 02, 2010, 09:23:21 am

It sounds like the parts sourced can handle (need?) a lot more current than the 20mA LED I prototype with. If it is just a matter of swapping the LED R value, then sure, it will be in any updates. I'd really like Seeed to use a plain plastic IR LED in the next batch, and I'll make sure it happens. I requested it in the current batch but they chose something else instead. I'm hoping with the increment we can revisit the bill of materials in more detail.

If anyone would like an R upgrade and can't do it themselves, just PM me and we'll arrange for a swap. The IR Toy is so small it can go in a bubble mailer with a single stamp, so it's not too big a deal to mail it around.

Re: Transmission distance is very short?

Reply #7 – September 07, 2010, 04:23:09 pm

Hi, all
My resitior R4 is 390ohm, and I replace it with a 39ohm one, and the valid transmission distance is about 300cm now. Thanks for all your help.

But there is still a big problem - the transmission angle! I will try to replace the IR LED with another one.

Re: Transmission distance is very short?

Reply #8 – September 07, 2010, 06:07:59 pm

The transmitter on mine is almost totally useless. Unless you strapped the irtoy to the receiever I don't think it will really pick up anything. I only really got a signal when the transmitter and receiver were about 10cm apart and direct line of sight.

Re: Transmission distance is very short?

Reply #9 – September 07, 2010, 06:23:25 pm

Yup, it's clear from rsdio's notes on the LED version in each batch that they are way under powered. The partlist specs a 20mA 'plain jane' IR LED, but the IR Toy has high power emitters that are underpowered. This is due to a footprint confusion in the first batch, and unknown reasons in additional batches (I requested the correct LED and am surprised to see them still shipping with the metal cased emitters, especially because they cost more).

I have not seen a manufactured IR Toy myself, so I'd be more than happy to take a look and replace the current limiting resistor. That offer goes to anyone, just PM me. It will also use the correct value on the updated hardware that I'm sending to you (just got the 18F's needed in this week).

Re: Transmission distance is very short?

Reply #10 – September 08, 2010, 03:51:16 am

[quote author="ian"]I requested the correct LED and am surprised to see them still shipping with the metal cased emitters, especially because they cost more.[/quote]Considering that they may have bought a reel of 1,000 of them, I can see why.  Except for the beam width, I see nothing wrong with the high-powered IR LED, since the SMD transistor is rated to handle the increased current (is that true on v1 and v1a?).

Re: Transmission distance is very short?

Reply #11 – September 08, 2010, 08:04:19 am

Yes, I believe a 1A NPN was used on both versions.

Re: Transmission distance is very short?

Reply #12 – September 29, 2010, 01:44:47 pm

Hi! I just got my Ir toy and noticed that I have the 200 mA IR LED. Wiki says it is for preorder1 only. Is this from the preorder1 that nobody ordered or is this a bonus for new orders?

I'd like to test the range of this toy, but don't yet have knowledge to play the ir codes with it. Anyone help?

Re: Transmission distance is very short?

Reply #13 – September 29, 2010, 01:53:32 pm

I think they continued to use the same LED.

The how-to shows an example of playing the codes in rawIO mode

Re: Transmission distance is very short?

Reply #14 – October 25, 2010, 04:50:26 pm

Replaced R4 with a 20 Ohm resistor. Not much improvement.

Replaced with IR-LED from old remote control: ~6 meters transmission range.

tl;dr The SFH-480 LED sucks.