Documentation

We have a winner. Test results in PCB test 2


LibreServo sending data via RS485 to Arduino plotter

After several tests, the LibreServo hardware is finally chosen and it's working, even the H-bridge that gave me a lot of problems! In general, all the parts of LibreServo remain as they were, because they were already working correctly, except the parts are discussed in this article.

New PCB Test v2 for LibreServo


Hello World in LibreServo PCB test v2

A month ago I was analyzing the results and conclusions obtained with the LibreServo test PCB v1 and trying not to lose momentum this month I have designed, I have ordered new PCBs and I have already assembled the LibreServo test PCB v2! 🥳

It is the first PCB that I have designed with 4 layers for LibreServo and I hope that this will mitigates some issues with the H-bridge that I think comes, in part, from electronic noise. For the rest, it is a PCB with the final components, it is closer to the final design in which I have forced myself to put the components as close as possible to each other to see the real limit between what is designed and what can be easily welded without overcomplicating things, everything holds up on paper but then you have to bring it to reality.

Results and conclusions of the tests

RS-485 9 Mbps Hello World
RS485 Hello World at 9 Mbps

After analyzing all the parts of LibreServo, I have decided to make several design changes again. I am happy with the results obtained with the test board since without it, it would have been impossible to analyze all the components separately and detect all the errors and faults that I have found, it is something that I should have done from the beginning and it would have saved me a lot of time. The topics to be discussed are:

  • Current Sensor
  • Protection against change of power polarity
  • New power supply, mpm3610 + ap2112
  • NTC temperature sensor
  • New more compact RGB led
  • RS-232 vs RS-485 serial communication
  • New AEAT-8800 magnetic sensor
  • H bridge
  • Next PCB (4 layers)

Power Analysis (MPM3610 + Ferrite + AP2112)

MPM3610 and AP2112 circuit with Ferrite MPM3610 and AP2112 circuit

One of the parts that I have changed the most in LibreServo and thought about is the power supplies. In previous versions it was a linear regulator that I reduced in size, but the truth is that I was not at all comfortable since if LibreServo was powered with only 12V, the linear regulator should dissipate up to 1.74 Watts and in 16v 2.54 Watts... something that was really unreal that it could handled.

A few months ago I discovered the MPM3610, and this finally made it possible for me to design the power supply as I wanted. This tiny component is a powerful 1.2A step-down that supports up to 21V input and also has a built-in diode and coil! It is the latter that makes it perfect for my design, due to the reduced space used, being the only step-down that is manufactured that has an integrated coil and diode in the same package. The difference between using a step-down and a linear regulator is that a linear regulator from 3.3V to 12V gives an efficiency of 35%, while a step-down of 80% or higher, the rest is dissipated in heat, so one is much more prone to overheating than the other. The downside of using a step-down is that they are quite noisy and their output is not as clean as one from a linear regulator.

Análisis del sensor de corriente ZXCT1010

Circuito básico ZXCT1010 con protección Zener MMSZ5226BS Circuito básico ZXCT1010 con protección Zener

El primer componente que voy a analizar en mi nueva placa para testear LibreServo es el sensor de corriente ZXCT1010, el cual es una versión mejorada del sensor ZXCT1009. La mejora sobre todo es en la parte baja del sensor, cuando hay poca caída en Rsense, parte en la que quería estar ya que no quiero que se desperdicie tensión en Rsense. Además, aparejado al sensor de corriente está el diodo Zener MMSZ5226BS para evitar que la tensión de salida del sensor de corriente pueda superar los 3,3V y quemar el microcontrolador.

New PCB to test LibreServo

LibreServo test PCB LibreServo test PCB

It has been a long time since my last update, a pandemic in between and many changes. Be that as it may, LibreServo continues moving forward, little by little, but it moves 💪.

During the previous versions of LibreServo I have continually encountered different problems in the design and without knowing exactly how different components were going to behave, in addition, later trying to debug the board being so compact and without extra space to be able to even solder a cable to be able to see the signs, always complicated everything too much.

Compras y cambios de los últimos meses en LibreServo

DS1054Z LA1010 GPS3010D DS3235 Nuevo material y herramientas para LibreServo

LibreServo va a sufrir varios cambios importantes y he decidido cambiar el método en el que estoy realizando las pruebas. Además, he decidido rascarme el bolsillo y comprarme algo más de equipamiento para medir todo lo necesario de una manera externa y precisa y así saber de antemano qué esperarme en LibreServo.

Nuevos diseños para el futuro

Encóder magnético vs potenciómetro

Llevo un tiempo dándole vueltas y desde el primer momento que me plantee LibreServo había un componente que me generaba dudas... el potenciómetro. En Selección de componentes para LibreServo ya lo comenté y hasta ahora siempre había más ventajas en utilizar el potenciómetro de Murata que un caro encóder magnético, al menos para una primera versión de LibreServo. Pero puede que eso haya cambiado.

"Magic Smoke" en LibreServo ¡Otra vez!

Estaba muy contento con el blanco del led Asmb-mtb0-0A3a2 y empecé a configurar el puerto serie.

El puerto serie debido a la altísima velocidad que puede alcanzar (9Mbps) hay que configurarlo mediante DMA, en otras palabras, que el envío y recepción de datos se haga en background sin usar ciclos de reloj de nuestro microcontrolador. El envío es fácil, pero la recepción requiere que se sepa de antemano el número de bytes a recibir... lo cual no sabemos. Habrá que darle alguna vuelta a la programación, pero tengo alguna idea.

Sea como fuere, primero empecé a configurar el puerto serie de transmisión, TX. Y tras unas pruebas... fumata blanca.

TX de LibreServo v1.c funcionando
TX de LibreServo v1.c funcionando

Resistencias para el LED RGB [Asmb-mtb0-0A3a2]

Tras muchísimos cálculos matemáticos... Todo se ha ido al garete y la realidad es bastante distinta a la calculada. ¡Menos mal que decidí comprar un montón de valores de resistencias para poder hacer las pruebas! El mayor problema que he tenido, es que el datasheet de Asmb-mtb0-0A3a2 no muestra dato alguno para cuando el led funciona a menos de 5mA, que es precisamente en el rango en el que funciona en LibreServo el LED.