Before I say anything, I want to urge you to consider disregarding any/all of this information, and choosing your own values for the oscillator components. A 40106 schmitt-trigger oscillator is purposely the simplest design I could find so that people might feel ok messing with the values and coming up with their own flavors. A grumpy old chef I used to work for had a saying that I’m going to pass on to you: “it’s a recipe, it’s not the gospel”. In that spirit, I’m going to offer you a very plain, average recipe that I expect you to experiment with and alter to your taste.
For inspiration, here’s a great page on designing schmitt trigger oscillators that has calculators for choosing component values & determining frequency.
NOTE: use some stand-off spacers or small washers when mounting the VGA tester to the PCB with the included stand-offs. They aren’t quite tall enough to fit the jacks underneath without a spacer.
As with the previous versions, this project is eminently hackable. For instance, if you’re a real lunatic, you could substitute photocells for all of the feedback resistors (R1, R2, R3, R4, R5, R8), and then you’d have a CHA/V that you could make suggestions to, but would basically have a mind of its own.
OK, fine, don’t listen. Here’s the recipe for a bland, mannerly CHA/Ves 3.xx that you wanted:
- Use 100k linear potentiometers for every oscillator. This will give you a nice, safe average range that isn’t too spicy and won’t upset anyone.
- Sync audio rate oscillators to [V] sync, video rate oscillators to [H] sync, and LFOs to [G] so they free-run. Remember, salad fork first, and no elbows on the table. Doing something like syncing video-rate oscillators to V sync would create uncivilized lines that simply will not be permitted at my dinner table.
- For LFOs, use 10uF timing caps and 10uF coupling caps. This value is the USDA recommended daily allowance and should not be exceeded.
- For audio-rate oscillators that make horizontal lines, use 0.1uF timing caps and 0.1uF coupling caps. Carefully check the expiration date of each capacitor before using it.
- For video-rate oscillators that make vertical lines, use 1000pF timing caps and 0.01uF coupling caps. No more than 8 ounces per oscillator.
TLDR bland CHA/V shopping list:
9x 3×2 pin header row
2x 4×1 pin header row
2x 1×12 pin header row
1x 1×9 pin header row
2x blue LED
4x 100K resistors (R6, R7, R9, R10)
6x 1k resistors (R1, R2, R3, R4, R5, R8)
2x BC547 npn transistor
1x 4001 rectifier diode (D2)
12x 4.7mm pitch spdt slide toggle switches (if you use flip-style instead, keep in mind that the pins will be inverted)
6x 100k linear PC mount potentiometers
1x 40106 hex Schmitt IC
1x 14-pin IC socket
3x PJ302m 3.5mm jacks
2x LDR, a.k.a. photo-resistors (LDR1, LDR2)
11x (or more) 2.54mm closed jumpers
10x (or more) 200mm socket-to-socket style jumper wires
4x 10uf electrolytic capacitors (C5, C15, C11, C23) negative leg should be pointing down. check oscillator 2 in the picture above. this part is not a joke: they could potentially explode if you put them in backwards.
4x 1uF ceramic capacitors (C4, C14, C10, C22)
13x 0.1 uF ceramic capacitors (C2, C20, C7, C17, C9, C21, C13, C25, C19)
4x 0.01 uF ceramic capacitors (C3, C16, C18, C24)
4x 1000 pF ceramic capacitors (C1, C6, C8, C12)
With these values, your oscillators will be arranged like this:
VCO2. lfo low/hi
VCO5: lfo low/hi