Inchworm 1.5 reed relay mod (Switched +5V on Target) - Electronic Circuits Projects Diagrams Free

blueroomelectronics · 23rd January 2007, 10:48 PM

I've been experimenting with one of my Inchworms and added a Radio Shack Reed Relay across RA4 (16F877 pin 6) and +5 (with a 1N4148 kickback diode) Two trace cuts (4.7K 1% *near the TP+5) and the +5V on CON1. I'll publish photos and info if anyone else needs this mod.

Would you like this mod in the next Inchworm design? Is it worth $5 extra?

**3v0** · 24th January 2007, 12:58 AM

Please post the mod.

Modify the board so it can be built both ways.
To build it without the relay have the user add jumpers in place of the relay.

That way you can keep the cost down and allow the relay to be added when/if needed.

If you would like help proofing the Robin Instructions PM me. Sounds like a neat device.

3v0

Sceadwian · 24th January 2007, 01:27 AM

Aren't Inchworms generally battery powered? Relays are more useful for line powered devices, I mean they're great on general purpose I/O boards but I'm not sure what you could use one for that you couldn't use a small H-bridge that would fit in close to the same space and be able to be switched faster and more reliably.

**3v0** · 24th January 2007, 02:18 AM

Quote:

Originally Posted by Sceadwian

Aren't Inchworms generally battery powered? ....

I was thinking inchworms were powered by bio matter...leaves.

Bill's ICD2 clone kit is named inchworm. But then you knew that..

3v0

lpinkai · 24th January 2007, 02:35 AM

William:

Sounds cool to me. Will this fix the MCLR issue (allow MCLR_off and internal oscillator on)?

-LP

blueroomelectronics · 24th January 2007, 03:06 AM

The mod functions to disconnect the +5V from the target CON1 (ICD2). I've not tried it with the mclr & intrc clk enabled although MPLAB still warns me not to. The relay coil (20ma) connects between +5 and the 16F877 RA4 (pin 6). The contacts connect to +5, R3 (top) and CON1 (+5V). A small 1N4148 diode should be added across the coil contacts (cathode to +5).
I can incorporate the relay or jumper mod into Inchworm II (PLCC 16F877A and PLCC 18F4550 optional) It will be slightly more expensive than the current Inchworm but upgradable to USB (just add the 18F4550, crystal and a couple of small parts) The 18F4550 is not a cheap chip.

gregmcc · 24th January 2007, 06:36 AM

Whats the function of this mod - you said it disconnects the 5V from CON1 - why not just not use the 5V when you connect CON1 to your pic circuit - what am I missing?

**Nigel Goodwin** · 24th January 2007, 09:21 AM

Quote:

Originally Posted by gregmcc

Whats the function of this mod - you said it disconnects the 5V from CON1 - why not just not use the 5V when you connect CON1 to your pic circuit - what am I missing?

Yes, you're missing the point!.

A programmer really needs to switch the 5V supply to the target device, which the InchWorm currently doesn't do - this restricts the config fuse options in devices like the 16F628 - where you can disable the MCLR pin and use it as I/O.

The ICD2 software already includes this facility, but it wasn't implemented in the InchWorm hardware.

gregmcc · 24th January 2007, 11:37 AM

Thought I was missing something - so it relates to the config bit topic which you replied to yesterday (http://www.electro-tech-online.com/m...-inchworm.html)

This could be a handy feature then!

evandude · 24th January 2007, 03:27 PM

Quote:

Originally Posted by blueroomelectronics

Would you like this mod in the next Inchworm design? Is it worth $5 extra?

If you shop around, you can find reed and/or DIP relays for more like $1-2. However, is there any reason you can't implement the same thing using a transistor, since you'll be changing the design anyway? I haven't delved into the details, but the USB ICD2 clone that I have just uses a PNP transistor to switch Vcc, according to the schematic.

Mike, K8LH · 24th January 2007, 04:01 PM

Seems like an awful lot of trouble and expense when all you need is a P-channel MOSFET and a resistor (or a PNP transistor and two resistors)? Duh!!!

(the two analog voltage divider resistors in the pic' below should already be on the board though they're probably connected to a "hard" 5v signal)...

blueroomelectronics · 25th January 2007, 02:21 AM

I'll look into the BS250P, you've posted it before I should learn to listen. I was concerned about the 230ma drive source be too small. Is there a 400ma pfet thats commonly available?
Thought #2 is use a PTC to limit current and remove the 7805 alltogether. So it's USB power plus RS232 (basic) and with the 18F4550 it's USB all the way.
Mike did you build a 18F4550 ICD2? I see there are some with a single 20MHz and some with 16MHz & 20MHz

Mike, K8LH · 26th January 2007, 02:08 PM

I only just started building my USB ICD2. I have stopped to consider adding the three 74LS12x parts so that I can support the 3.3v devices.

evandude · 26th January 2007, 02:33 PM

The USB ICD2 clone I built was from the PiCS rev B design at icd2clone.com - it uses a single 20MHz crystal. It doesn't have the buffers as some designs do, so it can't do the 3.3v parts, but I don't foresee myself using those any time in the near future anyway.

Mike, K8LH · 27th January 2007, 12:40 AM

That's the same design I started building too Evan (with a single 20-MHz crystal)...

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23rd January 2007, 10:48 PM	(permalink)
blueroomelectronics	Inchworm 1.5 reed relay mod (Switched +5V on Target) I've been experimenting with one of my Inchworms and added a Radio Shack Reed Relay across RA4 (16F877 pin 6) and +5 (with a 1N4148 kickback diode) Two trace cuts (4.7K 1% *near the TP+5) and the +5V on CON1. I'll publish photos and info if anyone else needs this mod. Would you like this mod in the next Inchworm design? Is it worth $5 extra? __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

24th January 2007, 12:58 AM	(permalink)
3v0	Please post the mod. Modify the board so it can be built both ways. To build it without the relay have the user add jumpers in place of the relay. That way you can keep the cost down and allow the relay to be added when/if needed. If you would like help proofing the Robin Instructions PM me. Sounds like a neat device. 3v0

24th January 2007, 01:27 AM	(permalink)
Sceadwian	Aren't Inchworms generally battery powered? Relays are more useful for line powered devices, I mean they're great on general purpose I/O boards but I'm not sure what you could use one for that you couldn't use a small H-bridge that would fit in close to the same space and be able to be switched faster and more reliably. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har."

24th January 2007, 02:35 AM	(permalink)
lpinkai	William: Sounds cool to me. Will this fix the MCLR issue (allow MCLR_off and internal oscillator on)? -LP

24th January 2007, 03:06 AM	(permalink)
blueroomelectronics	The mod functions to disconnect the +5V from the target CON1 (ICD2). I've not tried it with the mclr & intrc clk enabled although MPLAB still warns me not to. The relay coil (20ma) connects between +5 and the 16F877 RA4 (pin 6). The contacts connect to +5, R3 (top) and CON1 (+5V). A small 1N4148 diode should be added across the coil contacts (cathode to +5). I can incorporate the relay or jumper mod into Inchworm II (PLCC 16F877A and PLCC 18F4550 optional) It will be slightly more expensive than the current Inchworm but upgradable to USB (just add the 18F4550, crystal and a couple of small parts) The 18F4550 is not a cheap chip. __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

24th January 2007, 06:36 AM	(permalink)
gregmcc	Whats the function of this mod - you said it disconnects the 5V from CON1 - why not just not use the 5V when you connect CON1 to your pic circuit - what am I missing?

24th January 2007, 11:37 AM	(permalink)
gregmcc	Thought I was missing something - so it relates to the config bit topic which you replied to yesterday (http://www.electro-tech-online.com/m...-inchworm.html) This could be a handy feature then!

25th January 2007, 02:21 AM	(permalink)
blueroomelectronics	I'll look into the BS250P, you've posted it before I should learn to listen. I was concerned about the 230ma drive source be too small. Is there a 400ma pfet thats commonly available? Thought #2 is use a PTC to limit current and remove the 7805 alltogether. So it's USB power plus RS232 (basic) and with the 18F4550 it's USB all the way. Mike did you build a 18F4550 ICD2? I see there are some with a single 20MHz and some with 16MHz & 20MHz __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com

26th January 2007, 02:08 PM	(permalink)
Mike, K8LH	I only just started building my USB ICD2. I have stopped to consider adding the three 74LS12x parts so that I can support the 3.3v devices.

26th January 2007, 02:33 PM	(permalink)
evandude	The USB ICD2 clone I built was from the PiCS rev B design at icd2clone.com - it uses a single 20MHz crystal. It doesn't have the buffers as some designs do, so it can't do the 3.3v parts, but I don't foresee myself using those any time in the near future anyway. __________________ EEgeek.net

27th January 2007, 12:40 AM	(permalink)
Mike, K8LH	That's the same design I started building too Evan (with a single 20-MHz crystal)...