I am making an ultrasonic sensor board for my Arduino Uno R3 which I found a guide from here: A Cheap Ultrasonic Range Finder
The schematic is like below:
The problem is I couldn't find the transistor BD135 from my local suppliers, so I really need your help to suggest me some similar transistors which can be replaced for BD135.
It's an NPN transistor and it looks to me like it is very much overkill for this application. Why not just replace it with another NPN transistor and see how well it works? I don't see why a normal 2N3904 wouldn't work here.
330 uHy is a small dc resistance, were the duty cycle too high it could well destroy the transistor as theres no collector current limiting resistor present. An OK replacement would be a TIP41A. Although the current capacity is greater there should be no issues with your circuit. The beta is also relatively constant over the device operating range. Should work fine.
Who is your local supplier? Suitable replacements from mine (Maplins) are BD237 and TIP31C.
Any medium power npn should work, like the TIPxx family.
Do not add a resistor to the collector - that's just wrong.
Thanks for your help. I'll try your suggestion and feedback the result ASAP.