Let's Make Robots!

Ultrasound sensor from DAGU

Vendor's Description: 


Suitable for ASURO kits and any other kits



Part list:

6 x capacitor 100 nF ceramic
4 x resistor 10 kOhm ¼ W 5 %
1 x resistor 100 Ohm ¼ W 5 %
1 x resistor 1 kOhm ¼ W 5 %
1 x resistor 100 kOhm ¼ W 5 %
1 x resistor 20 kOhm ¼ W 5 %
1 x resistor 470 kOhm ¼ W 5 %
1 x potentiometer 1 MOhm
1 x ultrasonic transmitter 40kHz (400ST)
1 x ultrasonic receiver 40kHz (400SR)
1 x transistor BC547 or comparable
1 x diode 1N4148
1 x IC operational amplifier TS912IN or comparable

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First of all as a new member, hello from Copenhagen!

I got my package from Claudia in 2 days via DHL, great service. One of the items was this sonar sensor.  Since now we have the schematics and connection instructions in German ;) assembly is not that difficult. But I am a bit confused with the software part and I/O pins. AFAIK one pin is an input, which should be toggled at 40kHz to create the sound wave, then the comparator waits for the falling edge of the receiver and the signal time of flight is directly related to the distance to the object, right? But then why to use a comparator, can we just wait for the low signal on the receiver pin? Is it enough to use 4 pins i.e. VCC, GND, input 40kHz and output? which one are they on the board and what to do with the others? I guess they are customized for ASURO. As you can see I have still some doubts.

You need al least 2 prozessor pins to get the sensor working (and VCC, GND of cause). At Pin OC2 you put in a 40kHz chirp (burst of 40kHz pulses), then you count how long it takes to get an echo pulse at Pin ADC2.

There is a 3rd pin PD7 but I don't know it's function. In the Asuro software example it is declared as Input, but never used inside the code.  All other pins are Asuro specific. Also the breadboard for the kit is Asuro specific (some connectors are out of 0.1inch grid). So better use a simple breadboard and connect only the 4 used pins.

Compared with an SRF05 the results will not be very exactly. Some fine tuning and calibration must be done in Software and Hardware (potentiometer R10).

When your echo is recieved it's volume drops with distance and the size of the object. PD7 connects to C6 which is charged via D! when you generate your burst of sound. As the capacitor discharges via R9 the comparator within the atmega 8 (asuro's processor) compares the input from the sonar to C6's discharge curve and produces a digital pulse when the sonar input is higher than the discharge curve.

In this way the comparator works like a high gain amplifier as even the tiniest signal (as long as it's higher than the voltage on C6) will be amplified into a digital pulse.


Yikes!. I did not see this. Slowly I will learn, how this sensor works. For a comparator you need 2 analogue signals! Now I get it.

BTW. There are some differences between the schematic from Dagu and the german description and example code from Arexx NL. In the schmematic PD7 (AIN1) and ADC2 is used. In the description and Asuro sample code PD6 (AIN0) and ADC3 is used. I think the schematic is wrong because you cannot use AIN1 together with an ADC input.

I have grabbed out my ultrasonic sensor and tested it with my Asuro. It worked for a time when I build it, but one day it was no longer working. Yesterday I found a bad solder point and now its working again :-). I get accurate results in a range from 0..30cm, farer objects are not recognized. Maybe a amplifier for the sender will fix this behaviour.

Wow!! Is that really $6!! I will take the pain of assembling this rather than srf05! And there are still dozens of holes on the board for added customization! Where can we get this?

 Oddbot, looking frward for the walkthrough(maybe include 'comparator' crash course?). Thanks Claudia!

You can buy it directly from me, but the shipping cost is much expensive than the price itself.
Well.. shipping an SRF05 is not free either!

There is a detailed description for this kit including component layout, part list and C source code for the Asuro Atmel ATmega8 controller at the Arexx netherland homepage. Unfortunately only in german language.

Any Arduino board should work with this kit because it uses the same controller family.


The kits I got did not have the layout. Even though it is in German, the layout diagram makes it much easier to build.
The funny thing is, before I only have the layout plan and have to build the schematic out of this.