Getting to Know the "Professional ILC8038 Function Generator DIY Kit"

Intro: Getting to Know the "Professional ILC8038 Function Generator DIY Kit"

I was casting about for some new electronics projects when I came across a cute little function generator kit. It’s billed as the “Professional ILC8038 Function Generator Sine Triangle Square Wave DIY Kit” and is available from a number of vendors on eBay for 8 to 9 dollars (figure 1).

Figure 1. The Little Function Generator

It’s built around the Intersil ILC8038 waveform generator chip as the name implies. It’s a newer iteration of a function generator kit that’s been available from eBay or Amazon for a while. It looked interesting enough that I ordered one. First issue – the kit ships from China so there was the usual several weeks delay before I got it, but it did arrive in the time frame indicated.

The kit arrived intact and complete. The components all appeared genuine and the PCB and acrylic case were well made. Then I got to the instructions – BIG FAIL. The instructions, such as they were, looked like they were copied and reduced to fit on 5.75 x 8” piece of paper, which made many of the lines unintelligible (plus the fact they were written in pigeon English). The same three sections (sections 3,4 and 5) were printed on both front and back of the “instruction” sheet, no Section 1 or 2. This was unfortunate, because there was nothing to show which component value fit in which holes on the PCB .

I have written this Instructable for anyone with similar issues or other problems, or who is considering building this fine little kit. Step-by-step instructions are included not only for assembly but also use of the ILC8038 function generator.

STEP 1: How to Put It Together?

Many of the components can be intuitively placed by looking at the diagrams on the PCB (figure 2).

Figure 2. Printed Circuit Board

The barrel jack (JK1), 3 position terminal strip (JP3), IC sockets, jumper strips (JP1 and JP2), ICs U1 and U2, trimpots (R2 and R3), and the electrolytic capacitors can be placed with certainty, but the resistors, ceramic capacitors, ICs U3 and U4, and potentiometers (one has a different value than the other 3) are going to present a problem. If you have a sharp eye you may be able to read the designations of ICs and the color codes of the resistors in Figure 1. What we really need is better instructions or a good schematic. I was not able to find any good instructions on the internet, but I did find an image of a Chinese schematic. Fortunately, electronic symbols are pretty much universal and component values were in English (figure 3). ICs U2 and U4 were missing but I could pretty much fill in the gaps. I made a bill of materials (BOM), matching PCB components with their appropriate values, which is all you really need to assemble the kit. The BOM is included at the end of this Instructable.

In addition to the schematic and list of materials I have also provided step by step instructions on assembly and operation of this cool little function generator, so let’s get to it.

Figure 3. Schematic

STEP 2: Kit Assembly

1. Solder in all the inert components (IC sockets, jacks, jumpers, and terminals). Make sure the notch on the end of each IC socket aligns with the notch in its PCB diagram.

2. Solder the resistors, trimpots, and potentiometers. Be careful to get the 50kΩ potentiometer in the R5 position (AMP). The other potentiometers are all 5kΩ.

3. Solder the capacitors. The negative lead of each electrolytic goes through the hole in the shaded or hatched side of its PCB diagram.

4. Solder in IC U2 (WS78L09) and snap the other 3 ICs into their appropriate sockets, aligning the notches correctly.

5. (Optional step) Remove any excess rosin flux from the solder points with 95% ethanol (Everclear) or 99% isopropanol followed immediately by a distilled water rinse. Be sure to dry the board COMPLETELY before use.

6. That’s it. Assembly is finished.

Now for the acrylic case.

The protective paper peels off easily if each piece is soaked in hot water for a minute or two. The pieces don’t need to be glued together. (I did attach the two longer side pieces to the bottom with a little acrylic cement). Once all the tabs on the side pieces are seated in the slots of the top and bottom plates the four long screws provided will hold everything together.

The short 3Mx5mm screws and nuts are provided to attach the PCB to the bottom plate of the case. The screws are not long enough. I used 8mm screws initially, but then decided not to attach the PCB at all. It fits snugly in the case.

I opted not to remove the protective paper from the top plate of the case since it was printed with labels for the potentiometers, jumpers, and terminal strip (figure 4).

Figure 4. Assembled Kit

STEP 3: Operation

I used a small AC/DC adapter that provided 12 VDC/500mA to power the function generator. Don’t use anything higher than fifteen volts. My kit came with the frequency range jumper set to 50 - 500Hz and waveform jumper set to SIN. The other position was marked TAI but I suspect this was a misprint and should have been TRI for triangle.

Sine Wave

Plug the oscilloscope lead into the SIN/TAI position of the terminal strip and set the waveform jumper to SIN. I used the 50-500Hz range for most of the demonstrations below. I output a sine wave with P-P amplitude of ~5V and frequency of 100Hz using AMP (R5) and FREQ (R4). You may have to play around with the settings a bit until you get a trace on the oscilloscope. Adjust the two trimpots (R2 and R3) and then the DUTY potentiometer to optimize the shape of the sine wave. R2 modifies the top peak and R3 modifies the bottom peak of the sine wave. DUTY (R1) adjusts the left and right bias of the waveform. The first sine wave I generated is shown in figure 5. Not too bad. You can even calculate root mean square voltage if you are so inclined.

(Vrms = Vp-p * 0.35355). It is 1.77 volts for the sine wave in figure 5.

Figure 5. Sine Waveform

Frequency Check (optional)

The next thing I did was measure the maximum and minimum values I could get at each of the frequency ranges.

The results were:

5 Hz to 50Hz range: minimum 1Hz, maximum 71Hz

50Hz to 500Hz range: minimum 42Hz, maximum 588Hz

500Hz to 20kHz range: minimum 227Hz, maximum 22.7kHz

20kHz to 400kHz range: minimum, 31kHz, maximum 250kHz

Minimum for the 500Hz to 20kHz range and maximum for the 20 to 400kHz range were off from the printed values, but most everything else was in the ballpark.

Triangle Wave

Set the waveform jumper to TAI (TRI) and connect the oscilloscope to the TAI/SIN position of the terminal strip. The function generator produces good looking triangle waveforms with sharp peaks (figure 6).

Figure 6. Triangle Waveform

RAMP (Sawtooth) Wave

A reverse ramp wave can be obtained from a triangle wave by turning the DUTY potentiometer counterclockwise. I was not able to get a normal ramp wave by turning the potentiometer the other way. The signal was lost by turning the dial too far, so the leading edge of the wave was never quite perpendicular, and the descending part of the ramp showed a little concavity. Not a perfect sawtooth, but it is what it is (figure 7).

Figure 7. Ramp (Sawtooth) Waveform

Square Wave

Connect the oscilloscope lead to the middle position of the terminal block marked SQU to output a square wave (figure 8). The AMP (R5) and OFFSET (R6) potentiometers seemed to have no effect on the square wave. The voltage of the waveform produced was about the input voltage (12 volts). I should have removed the waveform jumper altogether to see if that improved things but that thought just now came to me.

Figure 8. Square Waveform

Duty Cycle

The duty cycle of the square wave can by changed with the DUTY potentiometer (R1), Turn the dial counterclockwise to shorten and clockwise to lengthen the duty cycle. There is a minor problem with DUTY. Changing the duty cycle also slightly changes the frequency, so it may have to be readjusted after the duty cycle is changed.

Duty Cycle = percent of time in the high state divided by the period of the square wave.

As an example, the square wave in figure 9 has a period of 10msec and is in the high state for 5msec (also in the low state for 5msec).

So, duty cycle = (5msec /10msec) *100 = 50%. Figures 10 and 11 show the duty cycle adjusted to 60% and 40%, respectively.

Figure 9. Duty Cycle = 50%

Figure 10. Duty Cycle = 60%

Figure 11. Duty Cycle = 40%

STEP 4: That's All, Folks

That’s about it for this Instructable. If you found it useful, go forth and build your own pocket function generator. You can have a lot of fun for 8 or 9 USD. Simple Circuit signing off.

STEP 5: ILC8038 Function Generator Bill of Materials (BOM)

Resistors

R1 Potentiometer 5kΩ DUTY

R2 Trimpot 100kΩ

R3 Trimpot 100kΩ

R4 Potentiometer 5kΩ FREQ

R5 Potentiometer 50kΩ AMP

R6 Potentiometer 5kΩ OFFSET

R7 Resistor 1kΩ

R8 Resistor 1kΩ

R9 Resistor 10kΩ

R10 Resistor 10kΩ

R11 Resistor 4.7kΩ

R12 Resistor 30kΩ

R13 Resistor 10kΩ

R14 Resistor 4.7kΩ

R15 Resistor 10kΩ

R16 Resistor 10kΩ

Integrated Circuits

U1 ICL8038 CCPD Precision Waveform Generator

U2 WS 78L09 Positive Voltage Regulator

U3 18MDSHY TL082CP JFET-Input Operational Amplifier

U4 7660S CPAZ Voltage Converter

Capacitors

C1 Ceramic 100nF

C2 Ceramic 100nF

C3 Ceramic 100pF

C4 Ceramic 2.2nF

C5 Ceramic 100nF

C6 Ceramic 1µF

C7 Ceramic 100nF

C8 Ceramic 100nF

C9 Ceramic 100nF

C10 Electrolytic 100µF

C11 Electrolytic 10µF

C12 Electrolytic 10µF

Jack, Jumpers, and Terminal

JK1 Barrel Jack

JP1 2 position jumper block TAI (TRI), SIN

JP2 4 position jumper block 5-50Hz, 50-500Hz, 500Hz-20kHz, 20kHz-400kHz

JP3 3 position terminal block GND, SQU, SIN/TAI (TRI)

Comments

[rgk]

UPDATED:

Overall, the kit does what it says, and serves my need for a mostly-sine-wave and triangle generator for little money. I had some issues, but in correcting those issues, I found some errata. You may or may not want to tinker your kit to match what I found.

I compared this circuit to the original Harris and Intersil datasheets for the ICL8038. There are some oddities in this kit that do not match the original notes.

In this kit, the duty cycle pot (R1) is a 5K linear pot and the resistors to either end of the pot are 1K. In the original notes, the resistors (R7 and R8) are 4.7K and the pot is 1K. This accounts for the extreme sensitivity of the duty cycle pot in the kit. I will replace this pot with a 1K when I get a new parts order.

Capacitor C2 (104) "decouples" the frequency voltage to ground. However, the original datasheets show C2 connected to the voltage supply to the ICL8038, not to ground. The actual ground wire on the PCB connects to ground at the ICL7660 output; this injects the 7660 switching noise on its ground into the frequency input, and seems to account for the frequency jitter I see. C2 should be removed from the PCB and soldered directly to pins 1 (CCW) and 2 (wiper) of the frequency pot. It is the voltage between the power supply pin of the 8038 and the frequency input that determines frequency, not the voltage to ground.

In the original datasheets, the frequency pot is 100K log; I suspect that changing R4 to a 5K, 10K, 50K or 100K log pot would linearize the frequency sweep.

The output for sine and triangle connects the output connector directly to the output pin of the opamp. It would possibly save an opamp replacement to cut the trace from the CCW pin of R5 (amplitude) and solder a 51 ohm resistor across the cut.

I received the more recent version of the kit. This differs only in that it has a resistor and LED that comes on when DC power is applied to the jack. The blasted LED is a high brightness blue LED that is nearly blinding. I changed R17 (4.7K) to a 10K and it's still bright enough to show through the paper backing on my kit's plastic covers.

My 7660 died all on its own. I have professional experience with the ICL7660. It is fragile; anything more than 10.000000V will kill it. I believe that the 9V regulator is an attempt to protect the 7660. There are several pin-for-pin replacements for the 7660. The 7662S and MAX1044 both come to mind. They fit in the same socket. If you have to replace your 7660 converter, do NOT buy a chip that is rated for a maximum power supply of less than 12V; the original is rated at 10V. Some replacements will work up to 15V.

Most replacements allow you to connect pin 1 to pin 8 and increase the oscillation frequency from the 3kHz (that mine had) up to 10kHz or higher. This reduces ripple on the +/-9V outputs. Check the datasheet on the chip you get if you replace yours.

The square wave output from the 8038 is annoying to me. It does indeed go from ground to the chip's supply voltage, as promised, but this is not well matched to the size or DC level of the sine and triangle waves.

I added on a CD40106 hex inverter running from ground and the input voltage to "buffer" the square wave output. I also made a 10K+10K voltage divider across the power supply and ran a 10K resistor from the output of the CD40106 to the junction of the two 10K's. This produces a square wave of about 1/3 of the power supply (i.e. 4V on a 12V power supply) that is centered on the power supply, just like the sine and triangle outputs. This square wave can be selected like the sine and triangle into the dual opamps, and then is manipulated by the opamps as to DC offset and amplitude. I find this much more convenient than the existing square wave.

Again, the kit does what it says it does. You might want to mod yours to make it more "polite".

[pemazzei]

Hello! Please , why they use the 7660S CPAZ Voltage Converter? It is very hard to find here in Brazil. We don´t have the kit but can use the circuito diagram to assemble one. Thanks for the help. Paulo, Brazil

[SimpleCircuit]

You can try ICL 7660Sby Renesas or ICL 7660CSA+ by Analog Devices/Maxin. I'm guessing any voltage converter with 12VDC and ~ 20mA output should work. The Renesas ICL 7660 chips are fairly common. They can be purchased from Digi-Key, Mouser, or Jameco Electronics on-line here in the U.S. and I'm pretty sure they all ship internationally. Cost is 2 to 3 USD per chip.

[pemazzei]

Hello, please one more help. The circuit diagram shown in your instructable doesn`t have the connections for the ICL7660 (U4) and the 9 V regulator 78L09 (U2). We don´t have the kit here and I will buy the components and make a printed board for the assembly. So, please, what are the connections for this two IC? Thank you very much for your attention. Best, Paulo, Brazil

[Ayman AdeI]

do you havr this circuti pcb to print it ?

[pemazzei]

Hello, No, I don´t have it. I need to complete de circuito diagram with the voltage regulators. The author´s diagram is lacking these two components:CL7660 and 7809. Do you have the complete circuit diagram for this function generator? Paulo, Brazil.

[Ayman AdeI]

sorry i don't have it too , but if i found it i will tell you

[pemazzei]

OK, thank you. Best regards, Paulo

[pemazzei]

OK. thanks for help. Best. Paulo, Brazil.

[pemazzei]

No, not yet. I think to make the PCB board but I think this is a "commecial kit" and I can´t show it here...
But I still need to know the connectios for the two regulators....
Vest regards,

[Ayman AdeI]

can you share pcb in pdf or word file to print it ?

[KingWhiskers]

Thanks for this Instructable. It will be a great help. I just received mine but it was poorly packed and suffered quite a bit of damage. IC pins bent, dip sockets pins bent, even two pins fallen out of the one socket. Managed to straighten them all and all I gotta do now is assemble it. Got a 50% reduction in price for the damage, just hope all the straightened bent bits work.

[SimpleCircuit]

Good luck!

[omyocd]

Thank you for these instructions. I wouldn't have been able to figure out the potentiometers without your help.