Posted Wed Jan 15, 2014, 1:02pm Subject: Re: DIY grinder timer with 0.1 sec resolution
My circuit is using binary code to set the time but "inverted". Timing resistors are active/connected into the circuit when particular dip switch is open. With non-binary rotary switches, you will need at least 2 (for seconds and decimals) + separate resistors for each position on both switches. You could limit seconds from 5 to 15 and use two 10-position switches. I'm not sure if coded hexadecimal or binary rotary switches will work in this circuit. I agree that timing should be easily adjustable without tilting the grinder and will mod it in the future (currently I have too many projects to complete).
dwRK Senior Member Joined: 14 Sep 2013 Posts: 92 Location: Houston Expertise: Just starting
Posted Wed Jan 15, 2014, 3:14pm Subject: Re: DIY grinder timer with 0.1 sec resolution
Sorry...didn't pay attention to your circuit earlier...
I think this "binary" business is in terms of dip operations only...i don't see the circuit as binary at all in the digital sense of 0 and 1
Its been a long time since I looked at a 555...the dip switches changes the resistance of the string...so there's probably a voltage reference and comparator somewhere...your circuit is probably quite unique...
rotary encoders won't work without further ic to decode
i'd keep the dip switches...but perhaps do this to give you +/- 0.5s...i would find a small vr, stick the shaft out through the hole you did for the portafilter switch, stick the switch behind the vr...but you'll have to build a rig behind assuming you have space...this way you can do two things though that hole and keep it tidy
Posted Thu Jan 16, 2014, 10:59am Subject: Re: DIY grinder timer with 0.1 sec resolution
Idea with a pot and switch is excellent. After checking my spares I found 2 suitable pots with push-on switches, enough for my home and work grinders. I will keep dip switch under the grinder for seconds and replace decimals switch with pot/switch combination. One pot reads 23k5 and another 24k66 so I have to calculate accordingly values for timing capacitor and resistors to get around 1 sec adjustment from the pot.
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