Some Helpful Circuits

I've made a lot of circuits for various things. Some of them are pretty simple. Some of them are kind of difficult. Some of them were inspired by others on the internet. Here are a few.


Fan Speed Control

I wanted a circuit to control the speed of a muffin fan. They will kind of average a PWM signal to produce a range of speeds. I searched around on the internet and found this idea. I like the 555 so I repackaged it and did a layout and here it is. I'm sorry, I no longer know who to credit properly with this idea but if you think its yours feel free to let me know. Find it Here


RS-232 Optical Interface


Sometimes you need to pass serial signals through noisy environments. You need to convert the serial electrical signals to light. Here is a circuit that does that. Caution: this is not the most inexpensive way to do it but it works very reliably. You might be able to find substitutes or surplus components like I did.
Serial Circuit
Full Size


Ground Fault Interrupter


When you use batteries or other electrical storage devices in machines you might need to monitor them for connection to the machine chassis. For instance in an electric vehicle with rather large storage capacity and lots of volts you might run the risk of a short to the chassis causing injury or a fire and would like to know about it before that happens. In this circuit, a voltage of up to 96 volts is monitored by a resistance bridge circuit. If the higher voltage circuit comes in contact with the low voltage circuit, a current will be detected. If this current exceeds a predetermined amount it will trip. This circuit also uses the 555 in a novel way as the comparator and latch.
GFI Circuit
Full Size


This circuit requires an isolated power supply that is common with the higher voltage and uses an optical isolator to send a signal back to the low voltage circuit. This power supply is shown in the board layout but not the schematic.
GFI Layout
Full Size


Stepper Driver For BASIC Stamp II

Here's a simple circuit using MOSFETS to drive a stepper motor. There are other ways to do it but if you have the transistors anyway... I needed to pull an 8mm movie film past a video camera to make a digitizer. This system seemed to fit the bill. I haven't built the machine yet but its in the queue of projects to complete someday. Here's the circuit.

The other half of this setup is a program to turn the transistors on in the proper sequence. I found a guy who teaches electronics and had a tutorial on the internet that did most of what I needed. I modified his program to receive commands over the serial port and it works very well. Find the modified program here.

All that's left to be done is build the machine and finish my c# program that digitizes and moves the film one frame at a time. I've done a little bit by hand and it really needs a motor. You can find a c# project to talk to the BS2 here.