After a long time I decided to start again on this project. Quickly it became clear that there were still a few problems whit this project.
The first problem I encountered was that the transistors started to oscillate and draw to much base current when the voltage started to get to low. The oscillations turned out to be caused by the shutdown circuit I placed on the main pcb. After I removed this circuit the oscillations where gone. But there was still the problem of the too big base current in the transistors. This I solved by added 2 resistors to each step of the output stage.
R4 is added in this circuit. Also there needs to be a 150 Ohm 2W resistor placed between this pcb and the base of the 2N3055.
After these modifications it turned out that the power supply became a bit unstable. Therefore I replaced it by a 16V laptop charger. For the microcontroller and displays I added a voltage regulator pcb to create the required 5V.
The cooling fans need 12V, so I added a second voltage regulator pcb with a 7812 voltage regulator (mounted on the big heat sink).
When I was coding the current measurement I noticed another problem. The base current was also measured. To fix this I added a new pcb based on a ZXCT1086E5TA to measure the current trough the positive lead. This measurement however has the disadvantage to only work above 3V. This I “solved” by adding a few lines in the code which put — on the ampere display when the voltage gets too low.
To connect this pcb to the main pcb I had to mod the main pcb a bit:
New circuit:
To get a stable measurement, I take the mean value of a number of samples. For this code, the pic I originally designed into the the project, turned out to be too slow. Therefore I replaced it with a PIC16F25K22 (pin compatible). This pic operates at 64Mhz.
The code:
'****************************************************************
'* Name : Dummyload *
'* Author : Stijn Coenen ElektronicaStynus.be *
'* Notice : Copyright (c) 2013 Stijn Coenen (Stynus) *
'* : All Rights Reserved *
'* Date : 01/05/2013 *
'* Version : 1.2 *
'****************************************************************
Device = 18F25K22
Include "Config_Fuses_1_2.bas"
Xtal = 16
'****************************************************************
'EN: Declarations
'NL: Declaraties
'Displays
Symbol Disp_klok = LATB.7
Symbol Temp_Data = LATB.2
Symbol Temp_Latch = LATB.1
Symbol Spanning_Data = LATB.4
Symbol Spanning_Latch = LATB.3
Symbol Stroom_Data = LATB.6
Symbol Stroom_Latch = LATB.5
'EN: Measurement values
'NL: Meetwaardes
Dim Temperatuur As Word
Dim Spanning As Word
Dim Stroom As Dword
Dim StroomFloat As Float
Dim StroomPrecies As Bit
Symbol N_Samp_T = 10 'Number of measuring samples; Aantal meetwaardes
Dim GemT[N_Samp_T] As Word 'Array that contains the samples; Array die de meetwaardes bevat
Symbol N_Samp_U = 15
Dim GemU[N_Samp_U] As Word
Symbol N_Samp_I = 15
Dim GemI[N_Samp_I] As Word
'EN: Display values
'NL: Display waardes
Dim DispTemp As Byte
Dim DispSpanning As Byte
Dim DispStroom As Byte
Dim DispArT[3] As Byte
Dim DispArU[3] As Byte
Dim DispArI[3] As Byte
Dim IntCase As Byte
Dim IntX As Byte
Dim IntDisp As Byte
Dim X As Byte
Dim Temp As Byte
'EN: Settings AD converter
'NL: Instellingen AD converter
Declare Adin_Res 10
Declare Adin_Tad FRC
Declare Adin_Stime 250
'EN: Connections 7 segment displays on the 74HC595 pcb's
'NL: Aansluitingen 7 segment displays aan de 74HC595 op de printjes
'dPecgbfa
Symbol Nul = %01001000 ' a '0
Symbol Een = %11101011 ' ##### '1
Symbol Twee = %01010010 ' # # '2
Symbol Drie = %01100010 ' f # g # b '3
Symbol Vier = %11100001 ' ##### '4
Symbol Vijf = %01100100 ' # # '5
Symbol Zes = %01000100 ' e # d # c '6
Symbol Zeven = %11101010 ' ##### '7
Symbol Acht = %01000000 '8
Symbol Negen = %01100000 '9
Symbol Uit = %11111111 'Out
Symbol Streep = %11110111 'Bar
'EN: Connections of the transistors On the 74HC595 pcb's
'NL: Aansluitingen Transistoren aan de 74HC595 op de printjes
Symbol disp1 = %00001100
Symbol disp2 = %00001010
Symbol disp3 = %00000110
'EN: Misc
'NL: Diverse
Symbol TMR0IF = INTCON.2
'Tris registers
TRISA = %00111011
TRISB = %00000000
TRISC = %11111111
All_Digital = true
On_Hardware_Interrupt GoTo Interrupts
'****************************************************************
Opstarten:
'EN: Set clock to 64 Mhz
'NL: klok instellen op 64 Mhz
OSCCON = %01110111
OSCCON2 = %11000111
Clear 'ram
'EN: Timer0 setup to drive the displays
'NL: Timer0 instellen om de displays aan te sturen
T0CON = %11000111
INTCON = %10100000
INTCON2 = %00000100
INTCON3 = %00000000
IPR1 = %00000000
IPR2 = %00000000
IPR3 = %00000000
IPR4 = %00000000
IPR5 = %00000000
'EN: Settings AD converter
'NL: Instellingen AD converter
ADCON1 = %00000000
ADCON2 = %10010111
GoTo Main
'****************************************************************
Interrupts:
Context Save
If TMR0IF = 1 Then
TMR0IF = 0 'Reset flag
TMR0L = 230' 'Preloard timer
'EN: Loading data for the display that is driven this interrupt
'NL: Data inladen voor het display dat deze interrupt wordt aangestuurd
DispTemp = DispArT[IntCase]
DispSpanning = DispArU[IntCase]
DispStroom = DispArI[IntCase]
'EN: Get the transistor settings and set the decimal point
'NL: Transistoren info uitlezen en de comma aanzetten
Select IntCase
Case 0
IntDisp = disp1
Case 1
IntDisp = disp2
DispTemp.6 = 0
DispSpanning.6 = 0
DispStroom.6 = StroomPrecies
Case 2
IntDisp = disp3
DispStroom.6 = StroomPrecies + 1
Case Else
IntDisp = 255
IntCase = 0
EndSelect
'EN: Outputting transistors data
'NL: Transistor data inklokken
For IntX = 0 To 7
Temp_Data = IntDisp.7
Spanning_Data = IntDisp.7
Stroom_Data = IntDisp.7
Disp_klok = 1
IntDisp = IntDisp * 2
Disp_klok = 0
Next
'EN: Outputting display data
'NL: Display data inklokken
For IntX = 0 To 7
Temp_Data = DispTemp.7
Spanning_Data = DispSpanning.7
Stroom_Data = DispStroom.7
Disp_klok = 1
DispTemp = DispTemp << 1
DispSpanning = DispSpanning << 1
DispStroom = DispStroom << 1
Disp_klok = 0
Next
'EN: Latch data to the outputs of the 74hc595 ic's
'NL: Data naar de uitgangen van de 74hc595 ic's latchen
Temp_Latch = 1
Spanning_Latch = 1
Stroom_Latch = 1
'EN: Set counter for next interrupt
'NL: Teller bijtellen voor volgende interrupt
Inc IntCase
If IntCase > 2 Then
IntCase = 0
EndIf
Temp_Latch = 0
Spanning_Latch = 0
Stroom_Latch = 0
EndIf
Context Restore
Return
'****************************************************************
Main:
While 1 = 1
'EN: Temperature measurement
'NL: Temperatuur meting
For X = (N_Samp_T - 1) To 1 Step -1
GemT[X] = GemT[X-1]
Next
Temperatuur = ADIn 1
Temperatuur = Temperatuur * 5
GemT[0] = Temperatuur / 9
Temperatuur = 0
For X = 0 To (N_Samp_T - 1)
Temperatuur = Temperatuur + GemT[X]
Next
Temperatuur = Temperatuur / N_Samp_T
'EN: Voltage measurement
'NL: Spannings meting
For X = (N_Samp_U - 1) To 1 Step -1
GemU[X] = GemU[X-1]
Next
Spanning = ADIn 0
GemU[0] = Spanning / 1.86
Spanning = 0
For X = 0 To (N_Samp_U - 1)
Spanning = Spanning + GemU[X]
Next
Spanning = Spanning / N_Samp_U
'EN: Current measurement
'NL: Stroom meting
For X = (N_Samp_I - 1) To 1 Step -1
GemI[X] = GemI[X-1]
Next
Stroom = ADIn 16
'EN: Setting the decimal point place
'NL: Plaats comma bepalen
If Stroom > 500 Then 'X.XX
StroomPrecies = 0
StroomFloat = Stroom * (5/1024) * 10
Else 'XX.X
StroomPrecies = 1
StroomFloat = Stroom * (5/1024) * 100
EndIf
StroomFloat = StroomFloat / 50
StroomFloat = StroomFloat / 0.005
GemI[0] = StroomFloat * 1.07
Stroom = 0
For X = 0 To (N_Samp_I - 1)
Stroom = Stroom + GemI[X]
Next
Stroom = Stroom / N_Samp_I
'EN: Calculate value's for on the display
'NL: Meetwaardes naar display berekenen
For X = 0 To 2
Temp = Dig Temperatuur, X
DispArT[X] = LRead Cijfers + Temp
Temp = Dig Spanning, X
DispArU[X] = LRead Cijfers + Temp
'EN: The ZXCT1086E5TA does Not work below 3V, so display bars when this happens
'NL: De ZXCT1086E5TA werkt niet onder de 3V, dus als dit gebeurt streepjes weergeven
If Spanning > 30 Then
Temp = Dig Stroom, X
DispArI[X] = LRead Cijfers + Temp
Else
DispArI[X] = Streep
EndIf
Next
'EN: Delay for slower display update
'NL: Wachten om het display niet te snel te updaten
DelayMS 75
Wend
'****************************************************************
Cijfers:-
LData Nul, Een, Twee, Drie, Vier, Vijf, Zes, Zeven, Acht, Negen, Uit, Streep
End
The dummyload working:
Files
Code file: Download
Hex file: Download
Dutch 
