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The New Boards

I have several new versions of the board. Each with it's own special traits. Most have onboard fuses that will protect the board in case of an overload and I have a prototype board that uses the Atmega 328 microcontroller for the front end and one that will restore the automatic function. I have test run all of these, except the prototypes, and they work, but the testing time is short and for the time being the original board is the only one that is tried and true.

This video describes each board and what makes it different. I have a small supply of each type and can make any of them, except the prototypes, upon request.

The Standard L293 board

Standard L293

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.

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The Standard L293 board with SMD components

Standard L293 SMD

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

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The Standard L293 board with 5X20 fuse onboard

Standard L293 Bigfuse

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.

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High current H-Bridge version using electronic components

H-bridge version
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

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High current H-Bridge version using relays

Relay version
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.

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Prototype Atmega 328 version

Atmega 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.

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Prototype Automatic version

Auto Versionj
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.

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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.

I am currently using the L293B, a higher current version of the ic in the boards that I ship. It 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.


Wiring Schematic for Standard, SMD and 5X20 Boards

Parts List for Standard Board

Wiring Schematic for Relay Board

Wiring Schematic for TC4420 H Bridge Board