Velleman K7200 Gerber file

[metal]

Just an little update on project, I've had the boards made and they look good quality only took less than 5 days to arrive from the date of the order.

I've built one board up and been testing it from a 24V PSU, A long the way there was on little error with one transistor foot print was incorrect, Which I checked and checked but this one must have slipped through the net. We live and learn. Not that it was to much trouble I just turned it around.

I've also be working on the front end on the digital part. I've attached a couple of photo's just to show if anyone is interested in following.

The code is almost completed, Just awaiting some more DAC's to arrive as I've only one at the moment but I can use this to get the voltage control working then swap to the current control. I've done it so that you cna use both pots and keypad to set the output voltage and current.

Brief description on how it work,
It use a 16way key pad to set the voltage on Channel 1 you press the * key once, Press it again and you move to channel 2 and a third press it aborts the input but outputs remain the same, This is the same for current but press # instead.
Once you have selected the channel, The voltage reading starts to flash then you can enter the voltage required and you can see the keypress your entering, once set this displays the set voltage along with the set current at the bottom as you can see.

I've got to work out the math's so when you enter 5.00v on the keypad the output voltage is matched the same.(this is on my working list).

Both channels will be isolated from each other and I shall be using    an SI8600 Chip(I2C isolator )so that I can use one display and controller for both.

More will follow soon and including a video of the digital part working.

wizpic, sure you are using proton GLCD lib, am I right? if so, what do you use for the fonts?

[Wizpic]

wizpic, sure you are using proton GLCD lib, am I right? if so, what do you use for the fonts?

No Shoot me down  , at the moment an Arduino Mega256 but may cut it down to a mini or uno providing I've got enough pins lol.

Now I'm looking into rotary encoder to set the Dac, Just looking for examples at the moment(this is the best way i learn) I know in the past when I've used an encoder I found that it misses steps and this one of the reason I chose the keypad and pots, But do like the idea of a encoder on the front end with a few buttons as memory buttons to set a set voltage, Looking at a more reliable solution, I have found a circuit that should improve the signal and make it cleaner shown in the image below.

Does any one have a working example or more reliable method , Just adjusting the voltage on the dac using an encoder ?
 

[metal]

          

I hate arduino so much, anyway, for the sake of good old days, here is mine, it doesn't miss dents, and it worked like a charm in Oct 2009! Nothing is connected to the pins of the rotary encoder other than the MCU pins and their internal pullups. The trick was to use the timer interrupt as a debounce method to overcome the bounces from mechanical contacts. You can guess the frequency by looking at the timer register values.

I attached the code adapted for WinAVR, IAR and cvAVR, you can tell when looking at the code. you are on your own to tweak the code for your arduino, but if you manage to make it work, it will be real good for your project. The QUADRATURE is to support a different rotary encoder so I don't remember which line in the directives should work for yours.

[Wizpic]

Thanks, I shall have a look at your code, I've been doing some playing around, I get the encoder code working nicely showing the increments of on on the serial monitor,

I then try to add my ADS1115 and MCP4725 and everything just gets screwed up and it no longer increments, the same if I only add the MCP4725 alone,  I shall carry on playing for a bit more before bedtime

It's all fun in learning and playing around 

[Old_but_Alive]

I have bought rotary encoders from Aliexpress. make sure its the 5 pin version, so it has the switch in addition to the rotary part



https://www.aliexpress.com/item/32947217301.html?spm=a2g0o.productlist.0.0.3e294e99ZIhsSM&algo_pvid=3fc6ce5a-eb91-495e-96ab-f43336b83354&algo_expid=3fc6ce5a-eb91-495e-96ab-f43336b83354-0&btsid=0b0a187b16055942410426434e15b4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

https://www.aliexpress.com/item/4001207874956.html?spm=a2g0o.productlist.0.0.3e294e99ZIhsSM&algo_pvid=3fc6ce5a-eb91-495e-96ab-f43336b83354&algo_expid=3fc6ce5a-eb91-495e-96ab-f43336b83354-2&btsid=0b0a187b16055942410426434e15b4&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

[Wizpic]

I've been working on this again and now have chosen to go with 1 or2 rotary encoders(not decided yet.), I can set the Dac output with it and had it hooked up to my PSU board and the results are great so far.

To get some ideas I've watched the of an over view on the Siglent SPD3303C power supply which uses a single rotary encoder and 3 buttons to set the output voltages and the amps on both channels along with a fine button.

Then another 4 buttons, 2 Buttons select channel 1 or 2, Then the other 2 Turn the output on/off, See pic below

I can add/worry about the memory buttons later once everything else is working. (if needed)

I like the way this is set up and works plus it looks easy to use and implement , Now this is where I'm a bit undecided on Method A or Method B.

Method A.
To keep the same the set up as it is in the pic below (keep the foot print and layout small on the front panel) ?

Method B.
To remove the channel1&2 select buttons and have 1 rotary encoder with 3 buttons , one to select  between the voltage and amps setting along with the 3rd for the fine settings for each channel ?

This is where I'd like some input, what would you do or prefer Method A or Method B  ?

[Sideshow Bob]

How will you attack the digital current/voltage settings?

[Wizpic]

How will you attack the digital current/voltage settings?

I shall be using 4 times MCP4725 as there easier to solder, then a TCP9548 to multiplex them and then using isolated 5v supply for the dac’s and will be using an SI8600 for the I2C bus

[Wizpic]

Just thought I'd post an update on my on going progress has it's taking longer than I thought to sort out the digital control side of things after people suggested using an rotary encoder.
I've now changed from an Arduino Mega 2560 to now using an ESP32 as the mega was getting slower, The only draw back is limited pins but for the LED'S for visual indication to let you know which and what channels you are adjusting, So now looking at an PCF8574 for those led's.

Has it stands at the moment, The actual PSU board and been finished and tested (only one channel so far), All good so far. The controller is almost there so far it has 9 buttons one rotary encoder. These buttons select between channels for setting current and voltage settings 4 in total for these, 2 Buttons to output's on/off, the button on the encoder is for selecting fine/coarse adjustments The other 2 are spare at the moment(but need to add a calibration function.

So far I'm using 2 x MCP4822 (12 bit Dac's), Digital SPI & I2C isolators, 2 MCP3426 (16 Bit ADC'S) then an PCF8574 port expander.

I have chosen to go back to the SPI 128*64 GLCD'S (but will be looking at the TFT'S displays, But want to get it working first).

I've taken all the voltages readings  for setting the voltage and current and implemented this into my code, So over the next few days I will be hooking it up and controlling one channel first to see how it goes.

Here are some photo's, Sorry about the rats nest as I want to get is nearly completed and tested before I design the PCB for it which I'm doing as I go along making connections. I know I need to get of the bred board as this will interfere with the readings.

One of the things I need to look at is setting the voltage on the PSU goes to 6.531 volts and the DAC can only go to 4.095 volts but I can add an op-amp to double the voltage but will need a bit of some thought as I still would like to use the 4095 steps or close as possible to maximize the full range of it. Ideas welcome lol
 

[Sideshow Bob]

Are you using the voltage DAC as reference for LM723C?

[Wizpic]

Are you using the voltage DAC as reference for LM723C?

Yeah I’ve tested it on adjusting the voltage but only up to 5v from the dac and output of power supply went to about 23 volts as I need to boost the dac voltage to get the full output voltage working really well better than I thought, at the end of the day this controller should be able to be added to any other power supply as the front end

[Sideshow Bob]

Yeah I’ve tested it on adjusting the voltage but only up to 5v from the dac and output of power supply went to about 23 volts as I need to boost the dac voltage to get the full output voltage working really well better than I thought, at the end of the day this controller should be able to be added to any other power supply as the front end

Take a look my conceptual power supply. The one you are building will be somewhat similar. In order to compensate for a slightly lower voltage reference you can increase the loop gain slightly (R1,R2) to give the voltage range you want

[Wizpic]

The only trouble with that I see, Is there is no current limit, The K7200 power supply is based on a good design old hat I know but works very well.
From What I can remember from initial testing controlling it from this controller is the little amount you can adjust the voltage. I have an old triple power supply that one channel failed and the second one is now playing up, Hence why I went back to the K7200 design as I know how to repair it if it breaks, I found a few schematics but nothing is close to the one I have that's failed, I did start to reverse engineer the PCB but thought it was to much hassle in the end,  I will be using everything including the case and power transformer from it.

I've been looking into increasing the voltage from the DAC using an op-amp and set the maximum voltage from the DAC to 3.5 and with the op-amp it will double it. This will a dual power supply once finished. It's been a lot of hard work in writing the software but also its been a load of fun and time passing in doing it. Hopefully over the next couple of day I will be hooking up the controller to the power supply :-)   

[Wizpic]

I could not wait any longer and while the wife is at work I decided to hook it up now  , So I can continue in getting the software side of things done.

I must say I'm really pleased with the result it works really well and over the moon with it, I can increment in 10Mv steps through to 1 volt steps also I hooked up the current control and this also works perfectly so all in all I'm making great progress  and can't wait to get to the PCB design for it.
Here is  a picture where you can see I set the output voltage to 10.00V and you can see on LCD1 is reading 10 volt, LCD2 slightly out has this is just hooked up to the same channel.
 

[Sideshow Bob]

The only trouble with that I see, Is there is no current limit, The K7200 power supply is based on a good design old hat I know but works very well.
From What I can remember from initial testing controlling it from this controller is the little amount you can adjust the voltage. I have an old triple power supply that one channel failed and the second one is now playing up, Hence why I went back to the K7200 design as I know how to repair it if it breaks, I found a few schematics but nothing is close to the one I have that's failed, I did start to reverse engineer the PCB but thought it was to much hassle in the end,  I will be using everything including the case and power transformer from it.

I've been looking into increasing the voltage from the DAC using an op-amp and set the maximum voltage from the DAC to 3.5 and with the op-amp it will double it. This will a dual power supply once finished. It's been a lot of hard work in writing the software but also its been a load of fun and time passing in doing it. Hopefully over the next couple of day I will be hooking up the controller to the power supply :-)   

I think you missed my point. The conceptual drawing was just to show the principal. That is also used in your power supply regarding voltage regulation.  The loop gain in you circuit is as far as I can see decided by the ratio of R5 and R23 as in a non inverting opamp amplifier setup. Just increase R5 and your loop gain will increase. No need to add any extra opamp

[Wizpic]

Sorry sideshow bob I see what you mean now and get it I shall look into this wifey back today and she’s the boss 

[Jagi]

To get some ideas I've watched the of an over view on the Siglent SPD3303C power supply which uses a single rotary encoder and 3 buttons to set the output voltages and the amps on both channels along with a fine button.

This is where I'd like some input, what would you do or prefer Method A or Method B  ?

You have some serious professional grade equipment at your disposal. I wish I had them (outside work). Coming to the point, of what is a better method, it all depends on how much hardware or software you are going to burden. Using multiple switches for selection is easy in software (a 4x4 matrix keypad is easy to interface), but then the cost of hardware is the burden.
If you use a rotary encoder with a switch in the center for selection, then the hardware is less, but then doing the software to recognize the rotary encoder interaction increases and making the appropriate menu is another task.
From my understanding of 20+ years in the electronics field, you could use a combination of both (similar to what has been done by SIGLENT).

[Sideshow Bob]

Sorry sideshow bob I see what you mean now and get it I shall look into this wifey back today and she’s the boss  

If you select a gain equal to say 8 you will be able to get (in theory that said) an output of 8*4.096 volt and each ADC bit will be worth 8mV of output voltage. If you use say a gain of ten. You will have each ADC bit be worth 10mV. This will of course make your output voltage calculation very simple. In this case you will not be able to use the full ADC range but as I see it it does not matter much for this application. Resistors do have tolerance. But you can add say a 100 ohm multiturn pot for calibration purpose

[Wizpic]

If you select a gain equal to say 8 you will be able to get (in theory that said) an output of 8*4.096 volt and each ADC bit will be worth 8mV of output voltage. If you use say a gain of ten. You will have each ADC bit be worth 10mV. This will of course make your output voltage calculation very simple. In this case you will not be able to use the full ADC range but as I see it it does not matter much for this application. Resistors do have tolerance. But you can add say a 100 ohm multiturn pot for calibration purpose

I've been looking into this and I've got to look into a bit more and study the data sheet of the LM723 for setting the value of the resistors to get it to work from 0-5V input onto R20.

But I may see a little problem, With the pot's wired up and set to zero volts going into R20 is 1.041volts and with it set to max I get 6.473 volts so that an operating window of 0 to 5.43 volts.
I had a working design in proteus and changed the value of R5 to 8K2 and I could get the full range of 0-30V output by supplying R20 with 0-5V input but you still need to start off at 1.041 volts on the input of R20 to start the output moving from 0 volt(anything before 1.041 volts noting happens on the output voltage) then having the 4.095 volts sat on the input at R20 I still get my 30 volts output but the operating window now is 3.054 volts which to me is less steps ?
I've not tried it in on my current set up, I'd rather get close to the values and get the full range of 0-4.095 volts on the input of R20 rather than start of at 1.041 volts in proteus then carry out the mods on the real board(just saves making a mess on my PCB with having to keep soldering and desoldserng values in/out),
I was going to up load the proteus file but Stupidly I went to renumber the values of components so it would of made it easier to cross refence of the original schematic but something has gone wrong as now I only get 3.85 volt output where as before the whole design was working in proteus, Hopefully I can find what I changed/moved or deleted a wire my mistake and then I can upload for others to have a play with if they wanted and you can see what I'm trying to explain.

When I looked into this sometime ago I could not work it out so it may be just easier to stick with the op-amp to increase the voltage but now you've mentioned about altering the value of R5 I like the challenge now and can't stop thinking about it 

[Sideshow Bob]

If you could upload a proteus project at least the analog version. Given that you allready have done the job that is, it could fun to tinker with. But that would require that the modell  for the LM723cn is accurate. Do you have any idea regarding this?
I have done some working with the LM723cn but that was over 10 years ago. What I did back then was to build an differential amplifier from a LM324 and place it over the current sense resistor. By varying the gain of this circuit. I could set a very low max current and still use a 0.1 ohm current sense resistor. I did this by putting the current sense pin to ground via a resistor and the current limit pin was fed by the differential amplifier. Also from what I can remember the output voltage could not go below 2 about volt. Is this correct still?
With a 12 bit ADC I would not worry about the output voltage resolution. With a resolution of 50 mV. You will only need 600 steps to get a 0 to 30 output voltage. If you plan to use rotary encoders for voltage settings. Perhaps it could be an idea to use switch to set a corsa or fine sensetivety for the encoders. In coarse mode the voltage could say go up/down in .5 volts step. But in the fine setting it could be 50 mV(as an example)
Edit: Pin numbers refer to metal can package in the picture!!!

[Wizpic]

Here is a working version of it, The current part does not seem to be able to supply more than 3 amps for some unknown reason in proteus but in real life I get the full 5amps.

the voltage side of things work in proteus as real life but may be slight difference  on the R20 readings compared to real life one, But a least I can play with this to get some where close

EDIT: Yeah on the controller side things I'm using and encoder with the button multiplying between 1,10,50,100 count's (not yet set just may need 2 of them but waiting to get it fully working first before I commit the correct values

[Sideshow Bob]

Here is a working version of it, The current part does not seem to be able to supply more than 3 amps for some unknown reason in proteus but in real life I get the full 5amps.

the voltage side of things work in proteus as real life but may be slight difference  on the R20 readings compared to real life one, But a least I can play with this to get some where close

EDIT: Yeah on the controller side things I'm using and encoder with the button multiplying between 1,10,50,100 count's (not yet set just may need 2 of them but waiting to get it fully working first before I commit the correct values

The more I look at this design. The more I see it kind of need some modernisation. Nothing real big but some deatails here and there. Like using a more modern pass transistor (2n3055). You may get away with using only one. And also perhaps implementing a precision high-side current-sense amplifier. This way you can use a quite low value shunt resistor like 50mOhm. If you can not find a 5 watt 50mOhm resistor use two 100mOhm. And also use a staI also think about doing something to the current limiter system. Replacing it with some opamps. By using a quad tl074 you can replace the 741 opamp

[Wizpic]

I’ve did some playing around with the R5 changed it to 11k and changed R20 to 430K and I can now Control the voltage from 0.5 to 4.096 volts to get near 32 volts out, I only changed R20 as I had to in proteus so not sure if that’s the correct way with R20.

I left everything as to the original with all the components as I was not sure if the digital control would work so if it did fail I still could use it has is, I intend to control the relay through software so I can remove the op-amp, I’m using a 0.01ihm (20watt)resistor for current sense and changed the 2N3055 to MJ3281A transistor.

Now that the digital controller is working better than expected I will update schematics and remove the components not needed

[Sideshow Bob]

I do not think R20 is needed at all. As the input on the LM723 should be high impedance like an opamp anyway. But place the DAC close to the regulator.

Posted on: January 03, 2021, 01:35:30 13:35 - Automerged
Funny now i see why you need some voltage input on the R20 in order to get something out at all. It uses pin 9 as output to controll the power transistor setup. pin 9 is the zener output (see figure in post 44). Normally you use pin 10 (vout) as output. My guess is that is done in order to get 0 volt as output on the power supply. LM723 does not go any lower than about 2 volt

[Wizpic]

Yeah that’s why they use 2 lm723’s one so that it can be made to go to zero controlling the volts and the second one for current, same again on the input of R28 for zero current I get 0.750 volts which gives a minimum current draw of around 10-15Mamps anything lower than 0.750 the current limit is always active, to obtain 5amps the voltage on R28 is 1.267 volts, I can take it higher to get more than 5amps but my transformers are rated at 6.5amps