The Experimental Boards

Back in 2022 there were 2 or 3 of the L293 driver chips that "let the smoke out" as they say, and ceased to function. Thinking that maybe I had pushed the design too close to the limits of the chip I decided to look for alternatives. As it turned out it appears that there was nothng wrong with the design but instead I was unfortunate enough to get a bad run of the chips, I have had no more failures.

During the time that I thought I had a design problem I decided to look for alternatives. On this page are several of the ideas that I had. Most all of them add an online fuse and a couple get away from the L293. They have all now been declaired obsolete except for the H-Bridge version which is my current manual controller board. It has a peak current of 6 Amps and I have deleted the fuse from the board. The standard 3 Amp fuse in the ground lead is adequate.

This video describes each board and what makes it different.

The Standard L293 board

This is the standard board redrawn with an onboard 1 Amp pico fuse. The fuse will generally be soldered to the board and cannot be changed without solder equipment. As an alternative the fuse can be installed in slip in connectors as in this photo.

The Standard L293 board with SMD components

This is the standard board redrawn using surface mount resisters and LEDs. It also includes an easily replaceable 5X20 1 Amp fuse.

The Standard L293 board with 5X20 fuse onboard

This is the standard board redrawn with an onboard 1 Amp removable 5X20 fuse. This advantage here is that the fuse can be easily replaced.

High current H-Bridge version using electronic components

This is a high current version that uses MOSFET driver chips and is capable of handling currents as high as 3 Amps. This is far outside the normal current draw but the controller will be protected in case of a bind in the mechanism or a failure of one of the limit switches. A 3 Amp pico fuse is installed on the board. It can be soldered to the board or installed in slip-in connectors. The idea for this H-Bridge type of motor drive is courtesy of Mr. Lewis Loflin at Bristolwatch.com.

High current H-Bridge version using relays

This version uses relays for the motor control. This is the way Delanair did it with their original "amplifier" and I used them on my first controller board some years back. These relays can carry a maximum current of 2 Amps and the board has a 2 Amp pico fuse onboard that can be soldered on the board or installed in slip-in connectors.

Prototype Atmega 328 version

This is a prototype for the newer Atmega 328 board. It uses the Atmega 328 as the front end and the L293 as the motor driver. I will be working on this as I have time. I learned how to use the Atmega 328 as a stand alone chip with the help of this AlexInFlatland video.

Prototype Automatic version

This version will return the automatic function to the system. It makes use of the thermister in the dash to control the temperature inside the car. I have one running in my car now, but it is very much still in the prototype stage. I will keep this updated and make the board available as soon as I am satisfied that it is ready for prime time.

Why New Boards?

Recently there was a failure of one of the L293 motor driver chips and that made me think that maybe I should search for alternatives. The L293D is listed for 600mA steady current and 1 Amp surge, which under normal conditions is more than enough to safely run the servo. The servo under normal conditions will draw ~250 mA steady current with a peak less than 300mA, only about half of the rated load. The failure was caused either by a defective chip, some part of the system binding or maybe a faulty limit switch. Any of these can overload the L293D.

The L293B, a higher current version of the ic has a running current of 1 Amp and a surge current of 1.2 Amps.

The motor driver has to be some type of H-Bridge, a circuit that will reverse the polarity of the voltage to the motor as needed to run the servo back and forth. Originally Delanair used relays for this job, so one of these boards uses relays and can carry a 2 Amp load. Another uses a pair of ICs that are MOSFET drivers that can be used alone to carry a load up to 3 Amps. There is also a board that restores the automatic function to the system. They all have onboard fuses.

In the Downloads section there are schematics for each type and a parts list for the standard board.