10/15 Update: 88 cents. That's just crazy. http://www.ebay.com/itm/New-Arduino-Ultrasonic-Module-HC-SR04-Distance-Sensor-Measuring-Transducer-/181849383810
08/14 UPDATE: Renaming the thread One-Buck Ultrasonic Sensor due to Price Drop: http://www.ebay.com/itm/New-Arduino-Ultrasonic-Module-HC-SR04-Distance-Sensor-Measuring-Transducer-HE-/400756229697
11/26/12 UPDATE: After a year, I finally changed the thread title from Four-Buck to Two-Buck: http://www.ebay.com/itm/New-Arduino-Ultrasonic-Module-HC-SR04-Distance-Sensor-Measuring-Transducer-Hot-/271040857767?pt=LH_DefaultDomain_0&hash=item3f1b4b46a7
I lied. $3.95 w/free shipping. Prices on these sensors have been plummeting recently and this is a new low.
I received several of these today, which I paid $4.50 for on October 29. They are pictured and described as SRF-04, which I have used before. 4 pin units. Not PING quality, but very nice. Main bad thing is that they take 2 I/O pins. One trigger, one echo. PING uses just one.
What I received today are newer 4-pin SRF-05 units. Never used these before, and the only info I have found in 10 minutes of searching is at
which implies that these can be used with just one pin, like a PING.
The pinouts on mine are labeled differently than either of these. Mine are labeled:
Vcc---Trig---Echo---OUT---GND so these are some variant or knockoff. I hooked one up to a BS2 tonight using 2-pin mode and it worked flawlessly. I'll request info from the seller about the OUT pin, might take a day to get a reply.
With luck, I'll find out that I can tie the OUT pin to ground and get to one pin mode.
Without any reply or luck, I may tie the OUT pin to ground and release the magic smoke.
So right now, I can't say if they function on one pin, or that the seller will continue to ship 05 units instead of 04's, but they are quite a bargain either way. I just ordered some more. I'm a gamblin' man.
"When you make a thing, a thing that is new, it is so complicated making it that it is bound to be ugly. But those that make it after you, they don’t have to worry about making it. And they can make it pretty, and so everybody can like it when others make it after you."
- Pablo Picasso