This week I assembled all the parts onto a perfboard after making a layout with ExpressPCB. I use the layout as a guide when assembling circuits on a perfboard. Once the circuit is proven to work I can make a PCB from the layout. In this case it’s only serving as a guide. After assembling the board and connecting all the external wiring and LEDs I tested the board out. I immediately found an error on pin 8 of the first 555 timer. I failed to connect it to the positive voltage rail! OOPS! After connecting pin 8 the circuit began to function but with a minor flaw. The LEDs connected to the drain of the MOSFETs are staying dimly lit between pulsing cycles. They should be out completely! This will require some troubleshooting on my part. The circuit worked perfectly fine on the breadboard. I’ll be double checking my schematic and the circuit and looking for a possible error. It could also be an issue with the capacitance of a breadboard. I’ve run into this type of thing before. Some breadboards act as a capacitor and can influence the behavior of a circuit.
It may be a problem with the way I’ve connected the MOSFET. Here’s is a great beginner’s guide to the MOSFET that helped me understand how they work.
If you have any thoughts on this problem and it’s possible cause please join in on the discussion on YouTube or here on the blog. Below you’ll find a schematic of the circuit, a picture of the circuit on the breadboard and of course this week’s video.
You’ll notice that I have a PNP connected to pin 3 of the first 555. It’s actually connected wrong but it somehow works to turn on the third 555! I’m scratchin my head on this one. I’ve revised this several times and this the current circuit. I now have a BC547 NPN transistor serving as a inverting buffer. This works great to turn on the 555 but I still have a problem with the MOSFET connected to that 555. When it’s connected the flashing stops.
Keep on hackin!