infra red bumper...

Hi, I'm going to use the schema provided here with Arduino, i.e. to replace the given pic with Atmega168 (my choice):

You can see the schema on this pic:

I'm confused with the value of C3, please tell me what is that there, the 4.7mk, I think it must be 4.7mF, but then what cap. voltage is preferred? Also, the power of R7 is the question, if to, say, get a 15k ohm?

Also, any comment on the schema is very welcome, to hopefully make a more accurate ir-bumper switch and if possible to use it in series for line follower.

C3 is 4.7uF, that is micro Farads. Not sure what you are asking about R7.

TSOP1738 is designed for PCM remote controls and not a good choice for non-remote applications as it will require pause (off) times in the IR beam. Look at TSOP4038 or TSOP58038 instead.

If you read the datasheet for these IR receivers you'll find suggested values for R7. Its presence is to reduce noise and in my experience is unnecessary.

Its presence is to reduce noise and in my experience is unnecessary.

No it is a pull up resistor for the open collector output. The actual value dosn't matter much, make it 4K7.

Thank you, now confusion points cleared

A problem solved and new problem arrived: I can't get neither TSOP4038 nor TSOP58038 locally, and I couldn't find them on eBay too (can't order by other means), while TSOP1738 is easily available locally.

Would you make other suggestion, may be a better, alternative schematic for a DIY infra red bumper switch out of your experience please?

I would like to use some 60 of them on an Arduino bot and I need to make them cheap.

By googling I came only to this one, found yet another schematic but that doesn't seem working.

I would like to use some 60 of them on an Arduino bot

How are you going to use them, the TSOP1738 requires a modulated signal at 38KHz but also this signal has to come in pulses, that is 10 cycles of the 38KHz on and 10 off. Therefore your software driving the LED has to do this, and that is what you will see at the receiver. Is this what you want? Will you be picking up this IR signal directly or through reflection?

By googling I came only to this one, found yet another schematic but that doesn't seem working.

Randomly trying schematics found on the web without actually understanding them seldom works. What about the software?

the schematic that I was originally going to use, has code at the end (for PIC actually) I thought to first build hardware and then convert it for Arduino.

Now after some more hours of searching seems making a diy ir bumper switch is not that much easy...I thought already there exist diy schematic for Arduino on tutorials but can't find such :(

I am still not clear what you mean by a bumper switch. Yes it detects when something is close to something, but in terms of the actual circuit are you proposing the IR emitter and IR sensor on the same unit and you detecting a reflection from some object? If so what sort of range? These are normally short range and don't need the sort of receiver you have been looking at.

Thank you Mike, I'm actually trying to find a solution for 2 things around infra red sensory:

  1. a small-range finder / ir proximity sensor, like from 3 to 15cm,
  2. a touch-less bumper switch to feel the robot hit a wall.

Just some minutes ago I found this tutorial on Arduino:

that seems will solve my bumper problem (I need cheap, and yet locally available, and I have QRD1114 in local stores).

I did a lot of googling but some nice sensors are not available like TSL257 and similar and have no time to order from eBay (need to make the bot ready in this week).

diy, cheap, range finder for around 15cm is under question, a candidate is here:

Edit: candidate:

yet googling is not that easy for me when technical, as English is not my native and sometimes long time passes till reseting mind for a set of new searching keywords :D

Would very appreciate to have any comment / link that helps.

That link says about the QRD1114

Because the sensor component simply measures IR intensity and is unaware of the light’s source, it is susceptible to false positives caused by outside sources

Is important, and that is what modulating you light source gives you, an immunity to some extent from interfering light. However as you are in a hurry than go with that and see how it pans out. Good luck.

Thanks, well I will isolate the sensor for now, and in future projects do more research to come to something more reliable.