DIY Soldering Station [part 4]

Hi everyone, anyone, who is still reading this 😦

Check out my latest version of the SSS (Smart Soldering Station – Yes, it sounds cool, doesn’t it?) on  GitHub.

1.Power supply:

In V1, I used a buck regulator to step down from 19V, and powered the logic parts. But it was so hard to filter noise out of the analog signal. Because the PIC used +5V as a REF+ and +5V in this case was not exactly 5V but has ripple all over it. That affected the final digital result.

In V2, I used the jelly bean LDO LM7812 and LM7805 to “step down”. What I worried before was the heat dissipating from them. But after testing for a long time, the 78XXs don’t even need any heatsinks because the load on them is low. The result is good, stable ADC readings.

2.Amplification:

In V1, I only used 1 compartment of the LM358. I thought that would be good enough. Actually, I still think so.

In V2, while routing the PCB, I decided to utilize the other compartment as well. Why not since it’s already there with no extra cost. The gain is 1 as the name is voltage follower. One good point of this voltage follower is it will less affect the analog signal since it input impedance is high and output impedance is low which mean it can charge the ADC C_HOLD faster.

3. Buttons and LEDs:

V2 has 2 more LEDs beside the power_ON and heating_en indicator. V2 also has 2 buttons integrated into the same pins for those LEDs. In this configuration, the pins can be configured as input or output. Those pins and also be used for USART communication with PC for debugging purpose.

 

4. Mosfet driving:

V2 used MOSFET IRLR2908 from IR (80V, 30A) in a small package D-PAK.

The PIC will drive MOSFET using this push-pull circuit:

Here R10 and D3 act as pull-down resistor for safety when the board is just turned on and the PIC is still “sleepy”. Final purpose is to protect the MOSFET.

Also D3 acts as an indicator for heater ON.

5. Other functions:

  • Realtime clock: added a 32768Hz to Timer1. I intended to use this to display a realtime clock while the soldering station is at standby. Actually this is not very necessary, we can derived 1Hz pulse from the main 20Mhz crystal easily.
  • Ambient temperature sensor: added IC TMP101 from TI. This Ambient temperature sensor uses I2C to communicate with PIC. I have not yet programmed this part.
  • Auto-standby timeout: after some adjustable time (0-99 minutes), with the iron on its stand, the SSS will auto-standby, ie. lower its temperature to 150 degree C. Or power-off the iron. I have not yet programmed this part.

So if you’re interested in this project, or you think something is wrong, some functions you think that would be nice to have, please let me know. Or you can just fork this project on GitHub to start your own code. Have fun!

 

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