I was going to use a 555 to modulate an IR LED @ 38khz. The environment will be a protected from elements, but not heat/cold. Temperature could range from 20 to 100 (-6 to 38c).
How stable would the 555 be? I read some theoretical posts on it loosing precision as it aged & temp changes. I understand that everything decays & is affected by temp...
So the question is would it be stable enough for 5 years? 5 months? 5 days? Or would an MCU (attiny84 or atmega328) be better? I'm out to use as little power as possible... we're talking brief periods (1 second of activity per interaction -- avg would be 2 interactions per day) The receiving end of the IR is an ATMega328 based board with a TSMP58000
The temperature effect would be on the input offset voltages
of the on-chip comparators - go check out the data sheets for the various sorts
of 555 (CMOS, bipolar, different manufacturer's versions). In general devices
with a lower offset automatically have lower temperature coefficient of offset
and lower long term drift of offset.
Just be sure to use a quality timing capacitor, something like polycarbonate or
PPS which has very low moisture absorbance.
daveyjones:
So the question is would it be stable enough for 5 years? 5 months? 5 days?
What is "stable enough" for you? Is 10% enough? Is 1% enough? Is 0.1% enough?
TSMP58000 can receive IR signals modulated in very wide range, 20 to 60 kHz. It is 300% change.
Timer 555 itself is quite stable. Variation of frequency more likely will be caused by variations in power supply voltage, and by variations in resistance and capacitance of the passive components. In a worst case you might expect few percent changes of frequency over time and temperature. Is it "stable enough"? The answer mainly depends on the program you use in Arduino.
I designed this Cmos 555 IR sender as part of a curling timer gate (5 meters).
It runs for ~60 hours (continious wave) on two NiMh AA batteries, and is used on the ice.
No stability problems with a common integrated IR receiver.
@MarkT - -thanks for that info & explanations -- very helpful. I am sure my 555 (NE555) is a cheap one, I will look at getting a more quality chip & capacitor.
@akouz - I really don't know what is "stable enough" means (so why did I use it?) a scope here shows a 38khz remote is actually modulating at 37.5khz, so if +/- 500 hz is generally accepted as "ok" then I guess that's what "stable enough" would mean to me... "Remains in the generally accepted range"
@wawa - Thanks Your implementation looks easy enough to build, thanks! -- Do I need to convert my 3.3v to 2.5v, or would the circuit run in lesser voltage ? And a really (uninformed) question - The 38khz Tune"; I am not familiar with that symbol. I assume all the single flat bars are ground?
Thank you! This is all great stuff! I really appreciate your help!
daveyjones:
I really don't know what is "stable enough" means (so why did I use it?) a scope here shows a 38khz remote is actually modulating at 37.5khz, so if +/- 500 hz is generally accepted as "ok" then I guess that's what "stable enough" would mean to me... "Remains in the generally accepted range"
You did not describe the task. What are you trying to achieve? Why did you choose TSMP58000? It is not very popular receiver because it suited for specific tasks. Please consider to use a standard IR receiver with embedded AGC, filter and demodulator, such as listed here: Vishay IR receivers
I chose it because of all the different IR receivers/learners/demodulators it seems to pick up an IR signal best. A lot of the others are very directional and/or the distance is not good.
Given the relative circuity simplicity and considering the cost of additional components that a 555 requires, doesn't an Attiny85 seem like a good alternative to the 555? - Scotty
scottyjr:
Given the relative circuity simplicity and considering the cost of additional components that a 555 requires, doesn't an Attiny85 seem like a good alternative to the 555? - Scotty
Well - that is the question -- is an attiny8x be more stable ? I have all the parts for a 555 circuit, so purely cost wise, either is the same for me.
Moreover, could I use the same arduino I'm using to receive the signal as sending it? (Academic/theoretical question really...)
the bigger question is what would use less power? a 555 sending 2second msg @ 38khz, or an attiny sending it?
daveyjones:
I chose it because of all the different IR receivers/learners/demodulators it seems to pick up an IR signal best. A lot of the others are very directional and/or the distance is not good.
Lets compare TSMP58000 with one of standard IR receivers, TSOP32S40F.
TSMP58000 sensitivity is 12 mW/m^2; TSOP32S40F sensitivity is about 100 times better, down to 0.08 mW/m^2 (see fig.12 of data sheet). Directivity graphs are very similar, see fig.2 and fig.11 respectively; I would say TSMP58000 is more directional.
daveyjones:
is an attiny8x be more stable ?
Apparently your task have no requirements to stability at all. Anything will go.
daveyjones: @wawa - Thanks Your implementation looks easy enough to build, thanks! -- Do I need to convert my 3.3v to 2.5v, or would the circuit run in lesser voltage ? And a really (uninformed) question - The 38khz Tune"; I am not familiar with that symbol. I assume all the single flat bars are ground?
Yes, the circuit will also work on 3.3volt.
The tune trimpot is to adjust the transmit frequency to exactly the same frequency as the receiver.
You will get the longest range if the receiver/transmitter frequencies match.
I think I used a PNA4601 as receiver, and had to tune to 36.7Khz.
The flat bars are indeed ground.
The second LED with the 330ohm resistor was just a battery indicator.
It can be removed if you wish. (reset still has to be connected to supply...)
This circuit will NOT work with a standard NE555. A Cmos 555 is needed.
Leo..
Thanks @Wawa -- I ordered a couple cmos555 yesterday with some other bits for an attiny1634 project...
I will do power usage tests with a barebones attiny84 & then with cmos555 and see which uses less power.
Thanks for your input/help; it is much appreciated.
No need to test that circuit.
I made a bunch of them, and they all work 100%.
A Cmos 555 runs on fumes.
Almost all the power goes to the IR LED.
The whole circuit uses ~30mA on a 3volt supply with a 33ohm current limiting resistor.
Not sure what you are going to do with the circuit.
This one works in continious mode, and was used for IR gates.
The receiver detected breaking the beam.
Leo..
On a point of terminology, and I'm happy to get corrected if I'm wrong...
daveyjones:
I was going to use a 555 to modulate an IR LED @ 38khz.
My understanding of the terminology is that the 38kHz is the carrier frequency, and it gets modulated by the message. The creation of the 38k wave is not, itself, the modulation.
Yes -- you are correct. I have been reading so many specs and one is reference something one way, and another yet a different way, or not a t all, at least directly ("All the parameters are in there, including the formual, you need to fill in the unknowns")
I'm just out to have a box (shoe box size) and put smething in it. It's job is to either alert the other person "something is there" or "empty" If it's not empty, ,lock it.
There will be lots of issues worked out under fire.
I was convinced (by an "other" forum member that "IR" was the solution -- so the box has lot of strategically placed IR LED's. and one receiver. The original theory (before I learned so much more) was to turn on each IRED and then check the receiver "is it coverded?" there's mail, send a radio packet and go to sleep. If it's not covered, repeat for each of the other LED's = using a mux to make the wiring a big easier.
I learned that just a n IRLED can be narrow beam as can the receiver.... I am fascinated how the dozens of pairs I have tried, all really don't work that well (my tv works from 30' away, past a tree. My IRToy picked up every light in the box... but the receiverI have is giving me fits -- it should see all th elights; so my problem must be i'm not sending properly modulated off 38khz.... "the things we learn"
If I could just extract the good guts from irtoy I'd use that instead of trying to figure this out. one day; I'll have that a-ha! moment and all IR problems will be easy to solve problems...