I know it’s been a couple of weeks (ish) since the last update, but that’s because I’ve been busy on things…
However, the good news is that the PPG build documentation and files are now ready, and have been for a couple of weeks.
They have been teste d& work with baseline Worlds of Wonder sensors, Uklta's DoT sensors and Heretik forge prototype sensor
Dropbox link is here (opens in new window) - Updated 18/12/2018
This is a very specific build for a very specific
body, which while the circuit can be transplanted and used in other
pewpew bodies it is missing a few things that were sacrificed in the
name of compactness.
1st is a button to trigger a ‘reload’ cycle, rather than turning it on & off again
2nd is more power/current going to the IR emitter to increase the output and increase the range.
The PPG circuit, with the lens assembly in the PPG
documentations manages around 30-35 meters, which while above the “in
universe” range of 25 meters, is low compared to some of the kit people use.
Personally I think this is quite a reasonable range
given how small they are, and how tiny the lens assembly is (16mm lens, 14mm effective due to
the mounting) – I’m not sure I’ve seen and kit one with less than a 25mm lens
before now – I could be wrong, but I don’t recall
seeing any.
So, there are two major “upgrades” that I consider crucial, and one optional one that I’m planning
1: Add a reload button
A button to trigger the reload cycle (Currently only triggered on power-up for the ppg) was easy enough to add - but the space just wasn't there in the PPG body. 1 button, 1 resistor and a quick change to the code and that was
sorted.
2: Increase output power/Lens size
Now, there are a couple of ways to increase the range for a IR based system such as this:
More Power to the emitter
Larger lens & lens assembly.
More Power to the emitter:
There are some IR emitters out there that can take
quite large amounts of current for quite a high powered output, but in
line with the design principles in my head I’m
wanting to keep the price down as much as
possible while keeping it as straightforward as possible(1) so I’m
avoiding some of the really snacky IR LED’s that can manage some serious
grunt…. But cost £3+ each…..
So, using the SFH4545-DWEW emitters (Often referred
to as Gherkins) we have an ideal peak current limit of 2amps. I
don’t want to go higher than this as even at the short pulse duration
in use it would risk damaging the LED (and
yes, I have blown a couple working on things)
The PPG’s have a nominal max of 800mA due to the restrictions of the AND gate transistors that modulate the carrier and hit signal together, and
the voltage regulator is rated to supply 1.5A
max anyway.
So, overall, I’m looking at something that can give a power output greater than 800mA but <= 2A max
I’m also going with a 7.2V supply – the idea being the things can be powered from a standard nicad rechargeable racing pack (2)
The limit of the voltage regulator can be avoided by having the Emitter LED connect directly to the battery power supply
This would then need something that can take the modulated hit/carrier signal and pulse the emitter at up to 2A
Enter the Mosfet.
After an exciting(3) evening of
trawling through datasheets following a tip from Dave I eventually
settled on these Partly because it ticked all the
requirements and partly because it wasn’t the £3
each of the originally suggested Mosfet
😊
If anything, the mosfet is a little bit of overkill, but it seemed to be a choice between overkill and not enough…. So…
Anyway, with the mosfet needing 1.5V to turn on, and
the Emitter needing 2.7V, running off of a 7.2V supply gave me
7.2-(2.7+1.5) = 3V to play with to drive the current through the
emitter. Add in a 1.5ohm (half Watt) resistor gives a nominal
3/1.5 = 2A peak through the emitter.
Perfect.
Ain’t getting much better than that without changing the emitter
😊
and can drop the current/output by changing to a 2ohm resistor (for
1.5Amp output) or 3 ohm resistor (For 1 amp output) – which give a
possible option of having a small SPDT switch to switch between
1.5ohm and 3ohm resistor for outdoor/indoor-close work to avoid too
much power output causing the beam to “splash” – It’s never fun to shoot
yourself… Usually it’s considered far more sporting to let the other
side do it.
To be fair, to be on the safe side I may use a 1.6 ohm resistor on future/production boards which will drop the current to 1.8Amp as that should give a little bit of wiggle room for those components that are outside the average.
Larger lens & lens assembly.
A larger lens & lens assembly is a fairly
simple principle – The larger the lens, the more light it can collect
and send “downrange”
I’m currently working on a 25mm lens & barrel
assembly, that using the test circuit I knocked together to focus a
barrel/lens assembly gives a nice clear spot on the side of the building
down the road – given the brightness of it(4), it’ll
go a lot further, but I kinda ran out of houses….. But that’s a good
60meteres, and the circuit used was not running at quite the same power.
Next stage is going to be get a barrel/lens
assembly printed that includes a picatiny rail mount so I can stuff the
thing into a Nerf body, ad a sight and find out just what it can do.
And then do the same with a 30 and 40mm lens, all the way up to 50mm.
Optional upgrade:
The one upgrade I’m considering optional at the
moment will be a more visual human interface for showing the ammunition
status – at present it’s a single LED that come son when the ammunition
is “empty” and flashes while reloading.
There are enough spare pins on the chip, that I
will be able to use one of the to talk to an external picaxe chip(5)
that has one job and that’s to display the ammunition status in a more
human interface friendly form, be it 2 digit 7 segment
LED display (ala aliens pulse rifle).
A bargraph display or anything similar.
As long as the
communication protocol between the chips is “standardized” then pretty
much the sky is the limit.
But other than that, I’ve not given that option much thought yet as it only cropped into the old melon this morning.
But then given I only finished the first verostrip prototype of the enhance board yesterday, I’m not surprised.
Ttfn
Ady
- Yes, I know if I switch to a pure PIC microprocessor, I can reduce a number of the components and do more via code, but it then also becomes to my mind more difficult to explain what each bit is doing, and harder for anyone to “remix” parts
- Yes, I know about LiPo batteries as well – but I’m not a fan in all honesty – I couldn’t say precisely why, but there you go.
- This word is a lie… It was dull… Very, very dull.. but necessary
- And taking into account the peak wavelength of the IR viewer I was using was not the same as the peak wavelength of the emitter, so it will seem not as bright as it actually is
- Or Pic later as I do plan on moving to Pics for a future project “Project Arcturus”
