HPT-01members.iinet.net.au/~peter31/hptimer/HPT-01-MAN-HW-V1.1.pdf · HPT-01 Hydroponic Timer...

HPT-01 Hydroponic Timer Documentation V1.1

Hardware

PAGE 1 of 19 © PMS 2019

HPT-01 Hydroponic Timer

Hardware Documentation V1.1

References:

PCB Version: 1.0

BOM Version: 1.1

Revision History Version Date Details

1.0 1-July-2019 First Edition

1.1 5-Sep-2019 Updates after customer review


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Table of Contents Revision History ...................................................................................................................................... 1

List of Figures .......................................................................................................................................... 3

List of Tables ........................................................................................................................................... 3

Introduction ............................................................................................................................................ 4

What is the HPT-01? ........................................................................................................................... 4

Which models of Raspberry Pi can I use the HPT-01 with? ................................................................ 4

Wireless? ............................................................................................................................................. 4

What does Cheap and Cheerful mean? .............................................................................................. 4

Does it need Software? ....................................................................................................................... 4

Is This for You? .................................................................................................................................... 4

Warnings ................................................................................................................................................. 5

System Overview .................................................................................................................................... 6

PCB .......................................................................................................................................................... 6

Components ............................................................................................................................................ 7

On-Board Power Supply .......................................................................................................................... 7

Relay Outputs .......................................................................................................................................... 8

Intended Use ....................................................................................................................................... 8

Relay Voltage Selector ........................................................................................................................ 9

Comparator Sensor Inputs .................................................................................................................... 10

Using an LM35DZ Temperature Sensor ............................................................................................ 11

Using a Switch to Ground ................................................................................................................. 11

Detecting a DC Voltage ..................................................................................................................... 12

Using a Potentiometer ...................................................................................................................... 12

Using an ORP-12 Light Sensor ........................................................................................................... 13

I2C Sensor Inputs .................................................................................................................................. 14

Using the AM2320 Temperature/Humidity Sensor .......................................................................... 14

Alarm Output ........................................................................................................................................ 15

Status LED ............................................................................................................................................. 15

Buttons .................................................................................................................................................. 15

Run .................................................................................................................................................... 15

Halt .................................................................................................................................................... 15

Test .................................................................................................................................................... 15

RPi Assembly ......................................................................................................................................... 16

Mounting the Pi on the bottom of the HPT-01 ................................................................................. 16


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Mounting the Pi on the top of the HPT-01 ....................................................................................... 16

Hardware Installation ........................................................................................................................... 17

System Ground .................................................................................................................................. 17

Appendix A - Mechanical Details .......................................................................................................... 18

Mounting........................................................................................................................................... 18

Board Details - Summary .................................................................................................................. 18

Board Drawing – Metric .................................................................................................................... 18

Board Drawing – Imperial ................................................................................................................. 19

List of Figures Figure 1 - HPT-01 Hydroponic Timer System Overview .......................................................................... 6

Figure 2 - HPT-01 PCB Rendered Image .................................................................................................. 7

Figure 3 - Example of a commercially available relay board .................................................................. 9

Figure 4 - Example of routed PCB around relay output common terminal ........................................... 9

Figure 5 - Relay Voltage Selector Header ............................................................................................. 10

Figure 6 - Rendered image of Sensor Input Circuitry ............................................................................ 10

Figure 7 - Wiring an LM35DZ to a Sensor Input .................................................................................... 11

Figure 8 - Wiring a switch to ground to a Sensor Input ........................................................................ 12

Figure 9 - Detecting a DC voltage .......................................................................................................... 12

Figure 10 - Using a potentiometer as a sensor ..................................................................................... 13

Figure 11 - Using an ORP-12 light sensor .............................................................................................. 13

Figure 12 – Wiring details for single/multiple I2C devices.................................................................... 14

Figure 13 - Using an AM2320 temperature/humidity sensor ............................................................... 14

Figure 14 - Connecting a 12VDC alarm sounder ................................................................................... 15

Figure 15 - Mechanical Drawing of the HPT-01 in metric units ............................................................ 18

Figure 16 - Mechanical Drawing of the HPT-01 in Imperial units ......................................................... 19

List of Tables Table 1 - Absolute Maximum Aux Current Supply .................................................................................. 8

Table 2 – Sensor Input Jumper Usage ................................................................................................... 11

Table 3 - HPT-01 Mechanical Dimensions ............................................................................................. 18


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Introduction

What is the HPT-01? It’s a PCA (Printed Circuit Assembly) which comprises sufficient electronics at low cost to control up

to eight relays on individual timers to operate a home hydroponic system. It includes four sensor

inputs which can be used to force relays to be on or off under software control.

It requires some basic electrical and computer knowledge to get it going, or the help of an assistant.

Hopefully this manual will help you and/or your friend through the setup and installation of the

timer.

Which models of Raspberry Pi can I use the HPT-01 with? Whilst the HPT-01 was designed to mount the Raspberry Pi Zero Wireless to it, you can use a

Raspberry Pi 3 if you can accommodate the mounting difference.

For the sake of clarity, whichever model of Raspberry Pi you use, it will be just referred to as the RPi

from hereon in.

Wireless? If you don’t have a wireless router, this isn’t for you. The project is designed to be cheap and

cheerful in comparison to other products on the market which are expensive and inflexible. That

includes using the cheap but powerful RPi as the only on-board computing power necessary for the

controller.

What does Cheap and Cheerful mean? It means engineering as much functionality into a low-cost project as possible, whilst keeping the

user interface as clean, accessible and intuitive as possible.

Does it need Software? Yes. Please see the Software manual.

Is This for You? If you can tick all of these boxes, then Yes!

Question

I have an Internet service

I have a Wi-Fi Router

My Hydroponic Timer will be placed within the router’s Wi-Fi range

I have a PC with a Web Browser

My PC has a slot for an SD card

I have an adaptor to fit a Micro SD card into my PC

I can understand downloading from the Internet

I can understand installing and running programs on my PC

I can edit a text file to change a section of text using written instructions

I have a Digital Voltmeter capable of 10mV resolution

I have a terminal screwdriver (3mm flat blade)

I have a small flat-blade screwdriver (2mm) to adjust trimmers

I feel competent to wire up electrical devices using mains power

I can take technical advice by email


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Warnings The following warnings are spread out among the manual pages, but it is recommended that you

familiarise yourself with them first.

Warning 1 - Do not connect a powered peripheral to the RPi USB ports .......................................... 7 Warning 2 - Do not exceed the Maximum Auxiliary Supply Currents ................................................ 8 Warning 3 - Do not connect the mains directly to the HPT-01 ........................................................... 8 Warning 4 - Relay output driver ratings ............................................................................................. 8 Warning 5 - Choose a relay board which has a routed slot around the relay common terminal ...... 8 Warning 6 - Relay Boards may need insulation on the mounting posts ............................................ 9 Warning 7 - Do not use the 3.3V Relay Voltage to drive a relay board .............................................. 9 Warning 8 - Maximum DC Voltage Sensing ...................................................................................... 12 Warning 9 – Maximum I2C sensor cable length ............................................................................... 14 Warning 10 - Beware shorting 12V to 5V ......................................................................................... 17 Warning 11 - Making a System Ground connection ......................................................................... 17


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System Overview Take a look at the system overview below in Figure 1. The HPT-01 is the orange part in the middle.

Figure 1 - HPT-01 Hydroponic Timer System Overview

The HPT-01 incorporates:

Internal 5V and 3.3V power supplies for the RPi and the PCB from an external 12VDC input

Mounting of a RPi Zero Wireless

A Darlington driver chip to control up to eight relays

Four threshold comparator inputs for connecting voltage sensors

A 12V alarm output for a low-current sounder

Screw terminals for all external connections

The HPT-01 DOES NOT include any of the green bits, which you must supply yourself. These are:

12VDC power supply rated at 1A or more

RPi

8G SD card for the RPi

A relay board with sufficient current and voltage capacity to control your electrics

An alarm sounder (12V, 100mA max), though there is a red LED

PCB See Figure 2 below for a rendered image of the PCB.


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Figure 2 - HPT-01 PCB Rendered Image

Components Nearly all the components on the HPT-01 are through-hole, to facilitate easy repair and

modification.

The 3.3V regulator is surface-mount (to allow the PCB to act as a heatsink) but the 5V regulator is a

switching type. The diodes are also surface-mount (if you've ever tried to replace a 1N1001 on a 2-

layer PCB with a ground plane, you will understand why).

All of the through-hole components are available from a local electronics store, and the two ICs are

socketed using quality turned-pin holders.

On-Board Power Supply The on-board power supply comprises a switching supply PCB for 5V and a following 3.3V linear

regulator, all derived from an external 12VDC power supply.

Only 5V is supplied to the RPi because it has its own regulators on board for lower voltages. Do not

connect a powered peripheral to the RPi.

Do not connect a powered peripheral to the RPi USB ports. Differences in Ground and +5V voltage rails may cause a failure.

Warning 1 - Do not connect a powered peripheral to the RPi USB ports

With no external current drawn, the 5V current is around 200mA to supply the RPi. The blocking

diode from the 12V input (to prevent a catastrophe if the supply is reversed) is rated at 2A.


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The 12V, 5V and 3.3V supply rails are available for external use on the Auxiliary PSU connector.

Whilst they aren’t expected to be of use in simple installations, they may be useful in some

circumstances. See Table 1 below for the maximum current resctictions.

Table 1 - Absolute Maximum Aux Current Supply

12V 500mA Continuous

5V 300mA Continuous

3.3V 100mA Continuous

Do not exceed the maximum current on any Auxiliary Voltage rail. Warning 2 - Do not exceed the Maximum Auxiliary Supply Currents

Relay Outputs There are eight relay outputs (numbered 0 to 7) available on a terminal block, along with Ground

and a supply called Relay Voltage.

Do not connect the mains directly to the HPT-01. Warning 3 - Do not connect the mains directly to the HPT-01

The output driver chip is the popular ULN2803 Darlington Driver, which sinks current to Ground.

Relay Outputs drive to Ground. Do not exceed 60mA per Relay Output.

Do not exceed 30V supply for any device driven directly. Warning 4 - Relay output driver ratings

Intended Use The intended use of these outputs is to drive the opto-isolated inputs of a commercially available

relay board which has a power connection and individual drive input along its length.

The current of each of these inputs is typically a few milliamps, though the relay board itself will

require a supply of some hundred milliamps to operate the relays themselves.

These relay boards are typically available in 5V and 12V supply models. See Figure 3 for an example

image of a commercially available relay board.

When choosing a relay board, it is important to choose one which has a routed gap around the relay

output common terminal, because it provides superior electrical isolation of the HPT-01 from the

mains (see Figure 4).

Choose a relay board which has a routed slot around the relay common terminal Warning 5 - Choose a relay board which has a routed slot around the relay common terminal


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Figure 3 - Example of a commercially available relay board

Figure 4 - Example of routed PCB around relay output

common terminal

Take care when mounting the Relay Board because some of them have tracks on top and underneath the mounting holes, which could cause a short

if you use metal stand-offs. If in doubt, use plastic fixings. Warning 6 - Relay Boards may need insulation on the mounting posts

Relay Voltage Selector The header RELAY_V connects one of 12V, 5V or 3.3V to the relay terminal voltage pin using a 0.1”

jumper (see Figure 5). It also connects the chosen rail to the free-wheeling diodes in the ULN2803 to

protect the transistors in the chip from inductive loads.

It is strongly recommended to use a relay board of the type described to simplify the wiring of your

system. Whilst the header is not explicitly labelled as to which jumper selects which voltage, it

follows the scheme of the Aux PSU Out test points directly above (leftmost is 3.3V, middle is 5V and

right is 12V).

DO NOT use the 3.3V setting to drive a 3.3V relay board! The 3.3V regulator will overheat. This supply is only intended for Solid State Relays.

Warning 7 - Do not use the 3.3V Relay Voltage to drive a relay board


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Figure 5 - Relay Voltage Selector Header

Comparator Sensor Inputs To keep in the spirit of Cheap and Cheerful, four sensor inputs (numbered 0 to 3) are available on-

board but as voltage comparators, not analogue values. For analogue values, please see I2C Inputs

in this section.

A comparator looks at an input voltage and compares it to a reference voltage. If the input voltage is

greater than the reference voltage, the software sees a 1, otherwise it sees a 0.

This may seem a little restrictive to people used to real-time, floating-point information, but it serves

most practical situations where you want to take an action based on a threshold setting which you

don’t need to keep changing.

Each comparator hardware block comprises:

A 3-pin terminal connection including Ground and 5V

A pin header to select the reference voltage range

A multi-turn potentiometer to adjust the reference voltage

A drain resistor

A sensor input circuit block looks like Figure 6 below.

Figure 6 - Rendered image of Sensor Input Circuitry

In use, connect the sensor input to the middle terminal and use the power supply on either side to

power it.

All the connections to sensors must go directly to the terminal blocks on the HPT-01 unless indicated

in the associated diagram.

There are five jumper selections, T, L, H, P and E, of which only a maximum of two are required for

each input. Their use is detailed in Table 2 below.


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Table 2 – Sensor Input Jumper Usage

JUMPER INSTALLED

T L H E P Ref. Voltage Range Typical Sensor Type 0.14 - 0.35 LM35DZ Temperature Sensor (14°C – 35°C) 0.00 - 0.22 LM35DZ Temperature Sensor (0°C – 22°C)

0.00 – 3.00 3.3V Potential Divider

0.00 – 5.00 5V Potential Divider

n/a Switch to Ground n/a Unused Input

To set the reference voltage, you need a volt meter capable of 10mV resolution to inspect the REF

test point, and a screwdriver to turn the potentiometer clockwise to raise the threshold voltage or

counter-clockwise to lower it.

Using an LM35DZ Temperature Sensor The LM35DZ temperature sensor is a 3-pin TO-92 device which can be powered from 5V and gives an

output of 10mV per degree Centigrade above 0oC. Please do not confuse it with other parts

available which are called LM35.

Wire the sensor to the HPT-01 using a wire length of 1.5m or less, being sure to insulate the LM35DZ

terminals after soldering the wires. See Figure 7 below for details.

Figure 7 - Wiring an LM35DZ to a Sensor Input

Jumper Setting Software Sensor Reading

T or T+E 1 if above the Reference Voltage, 0 if below

To set the temperature threshold on the HPT-01, set your voltmeter to mV and look at the voltage

from Ground (the test point at the bottom of U4) to the channel’s REF test point. Adjust the sensor

trimpot to (10 x oC) mV.

Using a Switch to Ground Fit the switch between the Ground and input terminals of the sensor terminal block on the HPT-01

and set the appropriate header jumpers. See Figure 8 below.


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Figure 8 - Wiring a switch to ground to a Sensor Input


H+P 1 if the switch is open, 0 if the switch is closed

Detecting a DC Voltage You may have electrics which operate independently of the HPT-01 and you want to know if they are

operating so you can change how the HPT-01 timers work. You can sense DC voltages up 24V using

the wiring in Figure 9 below. Please also see System Ground in the Installation section.

The maximum DC voltage that can be detected is 24VDC. Some voltages will require an external resistor.

Warning 8 - Maximum DC Voltage Sensing

Figure 9 - Detecting a DC voltage

Voltage to detect Value of Resistor

24V 22MΩ

12V 10MΩ

3V to 9V Not needed


H+E 1 if voltage present, 0 if not

Using a Potentiometer If you want to measure some property such as water level, using a float attached to a

potentiometer, you create a potential divider. It is recommended to use the 5V supply on the sensor

terminal block as the positive rail, but you can use 3.3V from the Aux PSU Out connector, or 12V if

need be. See Figure 10 below. Note that clockwise rotation increases the input voltage.


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Figure 10 - Using a potentiometer as a sensor


H+E 1 if above the Reference Voltage, 0 if below

Using an ORP-12 Light Sensor If you want to detect sunlight, you can use the cheap and popular ORP-12 light sensor. See Figure 11

below.

Figure 11 - Using an ORP-12 light sensor


H+P 1 if darker than the Reference Voltage, 0 if brighter


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I2C Sensor Inputs A terminal block is made available for connecting I2C sensor devices to in parallel. See Figure 12

below for details of how to wire I2C devices to the HPT-01. Note that the devices should be

connected in a string and not individually wired back to the I2C terminal connector.

Figure 12 – Wiring details for single/multiple I2C devices

The following I2C sensors are currently supported:

AM2320 Temperature/Humidity Sensor

Please advise your favourite devices and they can be added to the Scheduler Daemon if there is

sufficient demand!

The maximum recommended length of the entire I2C cable is 1m. Longer lengths may cause problems with sensor reliability.

Warning 9 – Maximum I2C sensor cable length

Using the AM2320 Temperature/Humidity Sensor This is a relatively cheap sensor (available from Adafruit) but is not terribly accurate according to the

datasheet, typically ±2oC and ±3% humidity. Validation testing showed that it is better than that, to

within 1% of both. See Figure 13 below for wiring details.

Figure 13 - Using an AM2320 temperature/humidity sensor


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Alarm Output The alarm can be configured by software to sound under certain conditions. A red LED illuminates

on the HPT-01, and if an external 12VDC sounder is attached it will provide an audible warning. See

Figure 14 below for connection details. Note that the sounder must be a DC type, not a simple piezo

device which requires modulation. The maximum alarm output current is 100mA.

Figure 14 - Connecting a 12VDC alarm sounder

Status LED The green STATUS LED is used under software control to indicate the operating state. See the

Software Manual for more information.

Buttons There are three buttons mounted on the HPT-01 called TEST, RUN and HALT. They may be either

surface mount or through-hole. See the Software Manual for more information.

Run The RUN button is a hardware input to the RPi and is the reason for fitting the extra 4-way header to

the RPi and HPT-01. When pressed, it will reset the RPi, or wake it up if halted.

Its main purpose is to restart the RPi if it is halted without having to remove and reconnect the 12V

supply.

Halt The HALT button is a GPIO input to the RPi and is used under software control to shut the RPi down

cleanly and safely if it is necessary to remove power to the HPT-01.

It is never recommended to just remove the power from any RPi without first shutting it down

properly.

Test The TEST button is another GPIO input to the RPi and is used under software control to perform a

test of the HPT-01.

Its implementation is software dependent.


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RPi Assembly You have two choices in mounting the RPi – on top or underneath. Some people prefer the RPi on

top for easy access to the SD card, but some people may need to mount it underside because their

RPi headers are mounted to the topside.

Please note that the nuts do not need to be anything more than finger-tight. The connectors hold

the RPi in place and the screws and nuts just have to stop vertical movement of the RPi.

Mounting the Pi on the bottom of the HPT-01 1. Solder the pin headers to the TOP of the RPi. Be sure that the smaller header aligns with the

larger one.

2. Insert the screws into the mounting holes from the top of the HPT-01 PCB and fix a nut from

the bottom side.

3. Fit another nut to each screw and turn it down to around 5mm from the PCB

4. Fit the RPi to the HPT-01 firmly and turn the latter nuts upward until they are flush with the

RPi

5. Fit the remaining nuts to the screws and tighten by hand

Mounting the Pi on the top of the HPT-01 1. Solder the pin headers to the BOTTOM of the RPi. Be sure that the smaller header aligns

with the larger one.

2. Insert the screws into the mounting holes from the underside of the HPT-01 PCB and fix a

nut from the top side.

3. Fit another nut to each screw and turn it down to around 5mm from the PCB

4. Fit the RPi to the HPT-01 firmly and turn the latter nuts downwards until they are flush with

the RPi

5. Fit the remaining nuts to the screws and tighten by hand


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Hardware Installation The recommended installation of the HPT-01 in a generous enclosure in a vertical orientation, with

the regulators topmost.

The relay board may be located up to a few metres away, however sensors should be kept to 1m, or

2m at the most.

When wiring into terminal blocks, it is necessary to turn off the power to the HPT-01 beforehand.

IF YOU SHORT 12V TO 5V AT ANY TIME, EVEN FOR A BRIEF PERIOD, YOUR RASPBERRY PI WILL BE BUGGERED.

Warning 10 - Beware shorting 12V to 5V

System Ground Things get very serious if your installation has more than one DC power supply because there can

only be one System Ground. Other power supplies that may be connected to the HPT-01 might be

powered by the mains, but their negative rails have to be connected together.

Ground is not the same as Earth. Do not connect Earth from the mains to this.

You must create a System Ground connection near your HPT-01 installation. This can be just a screw

and two washers with a nut to connect the wires to.

Make sure you connect all the local power supply Ground wires to the terminal.

You must make a System Ground Terminal in your installation if you have more than one DC power supply.

Warning 11 - Making a System Ground connection


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Appendix A - Mechanical Details

Mounting The HPT-01 PCB has 3.2mm mounting holes in each corner, suitable for M3 screws. There is

sufficient electrical and mechanical clearance for normal M3 mounting hardware to be used, such as

hex stand-offs and washers. The PCB was designed using Imperial units, so the metric equivalents

are correct to ±0.5mm.

Board Details - Summary Table 3 - HPT-01 Mechanical Dimensions

Dimension Inches mm

Length 4.45 113

Width 4.20 107

Mounting hole pitch - length 4.05 103

Mounting hole pitch - width 3.80 96

Board Drawing – Metric

Figure 15 - Mechanical Drawing of the HPT-01 in metric units


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Board Drawing – Imperial

Figure 16 - Mechanical Drawing of the HPT-01 in Imperial units

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