Can someone help me review this schematic? (AT89C52)

Thread Starter

redgear

Joined Oct 17, 2019
131
I am a beginner and I have got few questions with the first project I am attempting. I am trying to build a reliable timer circuit with three timing options. The use case is very similar to a microwave oven i.e., the circuit should check if the doors are closed, three timing options that can be selected with the buttons, start, stop and pause options for the timer.

I first thought of using a 556 timer(restricting to only two timing options) with a relay. But I also needed a display(lcd displays, not 7 segment leds) and it was not possible to interface a display with the 556 timer.
Another option was to go with a microcontroller like arduino which is easy to work with but I'm sure about the reliability. And they also cost more.
I was searching online and found this circuit for a microwave oven controller. I'm thinking to modify this to my needs than trying to build it from scratch. I have few questions:
  1. I am not able to find AT89C52, what else can I replace it with? Will any 8-bit 8051 do fine?
  2. I just need to control one relay and 5 input switches. Can I just leave the other ones floating?
  3. This circuit is designed to work with high power components while my total power usage will be around 80W, do I need to re-calculate for the resistors and capacitors?

Circuit-diagram-of-microwave-oven-1024x603.jpg


The circuit has no fuse on the AC lines. I will be adding a 5A fuse.

Thanks
 

Picbuster

Joined Dec 2, 2013
1,008
I am a beginner and I have got few questions with the first project I am attempting. I am trying to build a reliable timer circuit with three timing options. The use case is very similar to a microwave oven i.e., the circuit should check if the doors are closed, three timing options that can be selected with the buttons, start, stop and pause options for the timer.

I first thought of using a 556 timer(restricting to only two timing options) with a relay. But I also needed a display(lcd displays, not 7 segment leds) and it was not possible to interface a display with the 556 timer.
Another option was to go with a microcontroller like arduino which is easy to work with but I'm sure about the reliability. And they also cost more.
I was searching online and found this circuit for a microwave oven controller. I'm thinking to modify this to my needs than trying to build it from scratch. I have few questions:
  1. I am not able to find AT89C52, what else can I replace it with? Will any 8-bit 8051 do fine?
  2. I just need to control one relay and 5 input switches. Can I just leave the other ones floating?
  3. This circuit is designed to work with high power components while my total power usage will be around 80W, do I need to re-calculate for the resistors and capacitors?

View attachment 211400


The circuit has no fuse on the AC lines. I will be adding a 5A fuse.

Thanks
At the first glance I do see a problem with the rst circuit;
You try to put the rst switch parallel to a 10u Capacitor this need resistor in serial allowing power consumption when pressed.

Picbuster
 

Thread Starter

redgear

Joined Oct 17, 2019
131
At the first glance I do see a problem with the rst circuit;
You try to put the rst switch parallel to a 10u Capacitor this need resistor in serial allowing power consumption when pressed.

Picbuster
Thank you!
Does the rest of the circuit look fine? Do I not need to recalculate values for Caps and resistors if I plan to use it only for low power(~80W). Can I leave the connections to switches that I do not use floating?
 

absf

Joined Dec 29, 2010
1,947
I am a beginner and I have got few questions with the first project I am attempting. I am trying to build a reliable timer circuit with three timing options. The use case is very similar to a microwave oven i.e., the circuit should check if the doors are closed, three timing options that can be selected with the buttons, start, stop and pause options for the timer.

I first thought of using a 556 timer(restricting to only two timing options) with a relay. But I also needed a display(lcd displays, not 7 segment leds) and it was not possible to interface a display with the 556 timer.
Another option was to go with a microcontroller like arduino which is easy to work with but I'm sure about the reliability. And they also cost more.
I was searching online and found this circuit for a microwave oven controller. I'm thinking to modify this to my needs than trying to build it from scratch. I have few questions:
  1. I am not able to find AT89C52, what else can I replace it with? Will any 8-bit 8051 do fine?
  2. I just need to control one relay and 5 input switches. Can I just leave the other ones floating?
  3. This circuit is designed to work with high power components while my total power usage will be around 80W, do I need to re-calculate for the resistors and capacitors?

View attachment 211400


The circuit has no fuse on the AC lines. I will be adding a 5A fuse.

Thanks
I found your circuit from the EFY forum and the author also included the software in Keil C and Hex codes.

I recommend not to use the 89C52 as it does not support the ISP method of programming. You might have to program it with a DIY programmer interfaced to the PC parallel port.

Instead you can use the newer 89S52 from Atmel which supports ISP programming.

The link I found was HERE.
https://www.electronicsforu.com/electronics-projects/microwave-oven-control-board-2

Allen
 
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